What made you think that?
There seems to be some missguided believe that a 5900x somehow clocks better than 5800x. It made of the same CCD but on a 5900x there are two argueably lower quality ones due to the fact that 2 of the cores on each have been binned.
Just trawl through some of the threads on this forum and you can see the 5800x is getting consistently higher single and all core clock speeds over the 8 cores.
I think people are reading the headline specs but reality is different.
5900x is worse for gaming, all be it very marginally as your results found, but that is typical. Yet people are like, but 12 cores, 12 cores, 4 more cores, future proof, more cores........
Yup more core that for gaming, dont mean jack ****, today, in 5 years time or most likely 10 years time when the CPU will be more obsolete anyway.
Yeah but 12 cores.........
12 cores..........
The only justification anyone can legitimately have for needed a 5900x or a 5800x is they regularly use software that fully makes use of the multi-core threading, in which case fine.
But 12 cores, future proof.......