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Found the explanation for RTX 5090 and 5080 low compute performance. Link: https://videocardbenchmark.net/directCompute.html

We found out a few hours ago that nvidia removed OpenCL 32bit support. Seems it depended on CUDA 32bit. Which is also gone. We've been unable to buy a 5090 for testing (no stock locally). So couldn't test it. The 5090 failed with a non-obvious error code CL_OUT_OF_RESOURCES (-5) and nVidia didn't document the removal of OpenCL 32bit support. So it took us a while to understand the issue.

The nVidia web site still states 32bit (x86) is supported and gives 32bit (x86) code samples however. Link, https://developer.nvidia.com/opencl

The same code works fine on 4000 series cards.

Some of our 3D/compute sub-benchmarks are fairly small and don't need 64bit address space. So there was no need to port them to 64bit until now. Note that main PerformanceTest application has been 64bit for many years. So to fix this we will be needing to port the OpenCL code to 64bit, test for performance differences and do a patch release. This will of course break any OpenCL application that contains 32bit components. Likely many will never work on 5000 series cards. This might not be the only issue, as it doesn't explain the poor DirectX9 showing. But we'll be working on fixing OpenCL initially. So we expect the next patch release to show the 5000 series cards in a better light.