Have you investigated memory constraints?

Ryzen is 2 channels; Epyc is 4-8 (depending on CPU). M1 has that stupidly fast/wide setup.

If your Epyc is one of the 4 channel optimized SKUs or is only running in 4 channel mode, you would get pretty close to the quoted ratios on a memory bandwidth test.

Correlation, not causation, but worth looking into.

HN makes us wait for replies… so if we need to continue this further I’m open at muse.theses-0z@icloud.com .

My next question would be if you ran the 12900K in dual-channel memory.