diff --git a/applications/test/checkIOspeed/Make/files b/applications/test/checkIOspeed/Make/files
new file mode 100644
index 0000000000..67cce419cf
--- /dev/null
+++ b/applications/test/checkIOspeed/Make/files
@@ -0,0 +1,3 @@
+Test-checkIOspeed.cxx
+
+EXE = $(FOAM_USER_APPBIN)/Test-checkIOspeed
diff --git a/applications/test/checkIOspeed/Make/options b/applications/test/checkIOspeed/Make/options
new file mode 100644
index 0000000000..18b23366ad
--- /dev/null
+++ b/applications/test/checkIOspeed/Make/options
@@ -0,0 +1,7 @@
+EXE_INC = \
+    -I$(LIB_SRC)/finiteVolume/lnInclude \
+    -I$(LIB_SRC)/mesh/blockMesh/lnInclude
+
+EXE_LIBS = \
+    -lfiniteVolume \
+    -lblockMesh
diff --git a/applications/test/checkIOspeed/Test-checkIOspeed.cxx b/applications/test/checkIOspeed/Test-checkIOspeed.cxx
new file mode 100644
index 0000000000..a92159dde3
--- /dev/null
+++ b/applications/test/checkIOspeed/Test-checkIOspeed.cxx
@@ -0,0 +1,400 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | www.openfoam.com
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+    Copyright (C) 2024 OpenCFD Ltd.
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software: you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
+
+Application
+    Test-checkIOspeed
+
+Description
+    Simple test of file writing, including timings
+
+\*---------------------------------------------------------------------------*/
+
+#include "argList.H"
+#include "profiling.H"
+#include "clockTime.H"
+
+#include "fileName.H"
+#include "fileOperation.H"
+#include "IOstreams.H"
+#include "OSspecific.H"
+#include "globalIndex.H"
+#include "volFields.H"
+#include "IOField.H"
+#include "PDRblock.H"
+
+// Not really great since CoherentMesh only works with reading!
+#ifdef USE_COHERENT
+#include "OFCstream.H"
+#include "SliceStreamRepo.H"
+#endif
+
+#include <numeric>
+
+using namespace Foam;
+
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+// Main program:
+
+int main(int argc, char *argv[])
+{
+    argList::addNote("Rewrites fields multiple times");
+
+    argList::noFunctionObjects();  // Disallow function objects
+    argList::noCheckProcessorDirectories();
+
+    argList::addVerboseOption("additional verbosity");
+    argList::addOption
+    (
+        "output",
+        "N",
+        "Begin output iteration (default: 10000)"
+    );
+    argList::addOption
+    (
+        "count",
+        "N",
+        "Number of writes (default: 1)"
+    );
+    argList::addOption
+    (
+        "fields",
+        "N",
+        "Number of fields to write (default: 1)"
+    );
+    argList::addOption
+    (
+        "global",
+        "N",
+        "Global field size"
+    );
+    argList::addOption
+    (
+        "local",
+        "N",
+        "Local fields size (default: 1000)"
+    );
+    argList::addOption
+    (
+        "mesh",
+        "(nx ny nz)",
+        "Create with a mesh"
+    );
+    argList::addOption
+    (
+        "exclude",
+        "(int ... )",
+        "zero-sized on ranks with specified modulo"
+    );
+
+    argList::addBoolOption("coherent", "Force coherent output");
+
+    #include "setRootCase.H"
+    #include "createTime.H"
+
+    const label firstOutput = args.getOrDefault("output", 10000);
+    const label nOutput = args.getOrDefault("count", 1);
+    const label nFields = args.getOrDefault("fields", 1);
+    labelVector meshCells(0, 0, 0);
+
+    const int verbose = args.verbose();
+
+    const bool useCoherent = args.found("coherent");
+
+    labelList excludes;
+    args.readListIfPresent("exclude", excludes);
+
+    bool writeOnProc = true;
+
+    const label myProci = UPstream::myProcNo();
+
+    for (const label excl : excludes)
+    {
+        if (excl > 1 && myProci > 0 && (myProci % excl) == 0)
+        {
+            writeOnProc = false;
+            break;
+        }
+    }
+
+    const label nProcsEff =
+        returnReduce((writeOnProc ? 1 : 0), sumOp<label>());
+
+    Info<< "Output " << nProcsEff
+        << "/" << UPstream::nProcs()
+        << " ranks" << nl;
+
+
+    if (args.readIfPresent("mesh", meshCells))
+    {
+        if (!writeOnProc)
+        {
+            meshCells = Zero;
+        }
+
+        PDRblock block(boundBox(point::zero, point::one), meshCells);
+
+        // Advance time
+        // - coherent currently still needs to read the mesh itself!
+        runTime.setTime(firstOutput, firstOutput);
+
+        IOobject meshIO
+        (
+            polyMesh::defaultRegion,
+            runTime.timeName(),
+            runTime,
+            IOobject::NO_READ,
+            IOobject::NO_WRITE,
+            IOobject::NO_REGISTER
+        );
+
+        autoPtr<polyMesh> pmeshPtr(block.innerMesh(meshIO));
+
+        fvMesh mesh
+        (
+            meshIO,
+            pointField(pmeshPtr->points()),
+            faceList(pmeshPtr->faces()),
+            labelList(pmeshPtr->faceOwner()),
+            labelList(pmeshPtr->faceNeighbour())
+        );
+
+        pmeshPtr.reset(nullptr);
+
+        const label fieldSize = mesh.nCells();
+
+        const globalIndex giCells(fieldSize);
+
+        // Create fields
+        Info<< nl << "Create " << nFields << " fields" << nl
+            << "field-size:" << fieldSize
+            << " total-size:" << giCells.totalSize() << nl;
+
+        // Dimensioned field (no proc boundaries)
+
+        PtrList<volScalarField::Internal> fields(nFields);
+
+        {
+            IOobject io
+            (
+                "field",
+                runTime.timeName(),
+                runTime,
+                IOobject::NO_READ,
+                IOobject::NO_WRITE,
+                IOobject::NO_REGISTER
+            );
+
+            forAll(fields, fieldi)
+            {
+                io.resetHeader("field" + Foam::name(fieldi));
+
+                fields.set
+                (
+                    fieldi,
+                    new volScalarField::Internal(io, mesh, dimless)
+                );
+
+                auto& fld = fields[fieldi];
+                std::iota(fld.begin(), fld.end(), scalar(0));
+            }
+        }
+
+        IOstreamOption streamOpt(IOstreamOption::BINARY);
+
+        if (useCoherent)
+        {
+            #ifdef USE_COHERENT
+            streamOpt.format(IOstreamOption::COHERENT);
+            runTime.writeFormat(IOstreamOption::COHERENT);
+
+            mesh.writeObject(streamOpt, true);
+
+            Info<< nl
+                << "Specified -coherent (instance: "
+                << mesh.pointsInstance() << ")" << endl;
+
+            const auto& coherent = CoherentMesh::New(mesh);
+
+            Info<< "    points  = "
+                << coherent.globalPointOffsets().totalSize() << nl
+                << "    cells   = "
+                << coherent.globalCellOffsets().totalSize() << nl
+                << "    patches = "
+                << coherent.nNonProcessorPatches() << nl;
+
+            #else
+            Info<< "Warning: -coherent ignored" << nl;
+            #endif
+        }
+
+        Info<< nl
+            << "Writing " << nOutput << " times starting at "
+            << firstOutput << nl;
+
+        clockTime timing;
+
+        if (verbose) Info<< "Time:";
+
+        for
+        (
+            label timeIndex = firstOutput, count = 0;
+            count < nOutput;
+            ++timeIndex, ++count
+        )
+        {
+            runTime.setTime(timeIndex, timeIndex);
+            if (verbose) Info<< ' ' << runTime.timeName() << flush;
+            runTime.writeNow();
+
+            for (const auto& fld : fields)
+            {
+                fld.regIOobject::writeObject(streamOpt, writeOnProc);
+            }
+        }
+
+        if (useCoherent)
+        {
+            #ifdef USE_COHERENT
+            SliceStreamRepo::closeInstance();
+            #endif
+        }
+
+        if (verbose) Info<< nl;
+        Info<< nl << "Writing took "
+            << timing.timeIncrement() << "s" << endl;
+
+        Info<< nl
+            << "Cleanup newly generated files with" << nl << nl
+            << "    foamListTimes -rm -time "
+            << firstOutput << ":" << nl
+            << "    foamListTimes -processor -rm -time "
+            << firstOutput << ":" << nl;
+    }
+    else
+    {
+        label fieldSize = 1000;
+
+        if (args.readIfPresent("global", fieldSize))
+        {
+            fieldSize /= nProcsEff;
+        }
+        else
+        {
+            args.readIfPresent("local", fieldSize);
+        }
+
+        if (!writeOnProc)
+        {
+            fieldSize = 0;
+        }
+
+        const globalIndex giCells(fieldSize);
+
+        // Create fields
+        Info<< nl << "Create " << nFields << " fields" << nl
+            << "field-size:" << fieldSize
+            << " total-size:" << giCells.totalSize() << nl;
+
+
+        PtrList<IOField<scalar>> fields(nFields);
+
+        {
+            IOobject io
+            (
+                "field",
+                runTime.timeName(),
+                runTime,
+                IOobject::NO_READ,
+                IOobject::NO_WRITE,
+                IOobject::NO_REGISTER
+            );
+
+            forAll(fields, fieldi)
+            {
+                io.resetHeader("field" + Foam::name(fieldi));
+
+                fields.set
+                (
+                    fieldi,
+                    new IOField<scalar>(io, fieldSize)
+                );
+
+                auto& fld = fields[fieldi];
+                std::iota(fld.begin(), fld.end(), scalar(0));
+            }
+        }
+
+        IOstreamOption streamOpt(IOstreamOption::BINARY);
+
+        if (useCoherent)
+        {
+            Info<< "Warning: -coherent ignored" << nl;
+        }
+
+        Info<< nl
+            << "Writing " << nOutput << " times starting at "
+            << firstOutput << nl;
+
+        clockTime timing;
+
+        if (verbose) Info<< "Time:";
+
+        for
+        (
+            label timeIndex = firstOutput, count = 0;
+            count < nOutput;
+            ++timeIndex, ++count
+        )
+        {
+            runTime.setTime(timeIndex, timeIndex);
+            if (verbose) Info<< ' ' << runTime.timeName() << flush;
+            runTime.writeNow();
+
+            for (const auto& fld : fields)
+            {
+                fld.regIOobject::writeObject(streamOpt, writeOnProc);
+            }
+        }
+
+        if (verbose) Info<< nl;
+        Info<< nl << "Writing took "
+            << timing.timeIncrement() << "s" << endl;
+
+        Info<< nl
+            << "Cleanup newly generated files with" << nl << nl
+            << "    foamListTimes -rm -time "
+            << firstOutput << ":" << nl
+            << "    foamListTimes -processor -rm -time "
+            << firstOutput << ":" << nl;
+    }
+
+
+    Info<< "\nEnd\n" << endl;
+    return 0;
+}
+
+
+// ************************************************************************* //
diff --git a/applications/test/fileHandler-writing/Make/files b/applications/test/fileHandler-writing/Make/files
index f85b2cccec..df7161d2b9 100644
--- a/applications/test/fileHandler-writing/Make/files
+++ b/applications/test/fileHandler-writing/Make/files
@@ -1,3 +1,3 @@
-Test-fileHandler-writing.C
+Test-fileHandler-writing.cxx
 
 EXE = $(FOAM_USER_APPBIN)/Test-fileHandler-writing
diff --git a/applications/test/fileHandler-writing/Test-fileHandler-writing.C b/applications/test/fileHandler-writing/Test-fileHandler-writing.cxx
similarity index 95%
rename from applications/test/fileHandler-writing/Test-fileHandler-writing.C
rename to applications/test/fileHandler-writing/Test-fileHandler-writing.cxx
index 03caeab26d..a029befb7b 100644
--- a/applications/test/fileHandler-writing/Test-fileHandler-writing.C
+++ b/applications/test/fileHandler-writing/Test-fileHandler-writing.cxx
@@ -56,8 +56,18 @@ int main(int argc, char *argv[])
 
     argList::noFunctionObjects();  // Disallow function objects
     argList::addVerboseOption("additional verbosity");
-    argList::addOption("output", "Begin output iteration (default: 10000)");
-    argList::addOption("count", "Number of writes (default: 1)");
+    argList::addOption
+    (
+        "output",
+        "N",
+        "Begin output iteration (default: 10000)"
+    );
+    argList::addOption
+    (
+        "count",
+        "N",
+        "Number of writes (default: 1)"
+    );
 
     #include "setRootCase.H"
     #include "createTime.H"