On average according to Geekbench, the M5 compared to the 9950X is ~17% faster in single thread performance and ~30% slower in multithread performance.

Individual benchmarks tell the bigger picture. These two are optimized for different use cases, with Apple heavily leaning towards low latency single thread throughput with low sustained power usage.

https://browser.geekbench.com/v6/cpu/compare/16833358?baseli...

EDIT: The M4 Max compares much more closely https://browser.geekbench.com/v6/cpu/compare/16834801?baseli...