Tested with the benchmark (YMMV)
My setup: 6/12 core i7 6800k cpu, rtx 3090 gpu, 24gb ram. Benchmark set to: 1440p windowed, max settings, gsync disabled.

Scores:
16433 - 12 cores, All bios settings at default
16699 - 6 cores (hyper-threading disabled in bios)
15321 - 4 cores (2 cores disabled in bios)
11803 - 2 cores (4 cores disabled in bios)

So no difference at all between 12 and 6 cores, and only a fairly mild one between 4 and 6 (possibly due to the system being able to offload background processes).

This is pretty typical for games and why single core performance is emphasized for gaming builds.