Just got my x299 Dark system up and running and started playing around with overclocking my i9 7900x.
I noticed I was hitting thermal limits pretty quick even with a custom loop when exceeding 4.3Ghz (haven't delidded).
Because my primary workload is gaming, I decided to set a per-core multiplier on my two strongest cores to be significantly higher than the other 8.
Per-Core Multipliers (100 BCLK):
Core 0: 42
Core 1: 50
Core 2: 42
Core 3: 42
Core 4: 42
Core 5: 42
Core 6: 50
Core 7: 42
Core 8: 42
Core 9: 42
While doing stability testing in Prime95 I noticed something really interesting - all of my cores were hitting up to 4.7 GHz (even though most of them were set to a max multiplier of 42 (4.2 GHz).
After digging around a little bit (and realizing that Prime95 utilizes AVX by default) I noticed my AVX workload multiplier offset was -3. This explains the 4.7 GHz on Cores 1 & 6, but not all the others.
For testing, I set my AVX offset to -10 and rebooted. Running Prime95 again yielded some interesting results - all my cores held at 4.0 GHz. From this I can gather that when setting per-core multipliers, the AVX offset applies to the highest multiplier. Interestingly enough this allows cores with multipliers below the highest to exceed their set multiplier (assuming the max core multiplier - offset > core set multiplier).
TLDR: The AVX workload multiplier offset is applied to the highest core multiplier and then set for all cores.