Just asked.

https://www.reddit.com/r/intel/s/dWTgYuiHzU

That’s a cooling problem. Bad contact or dead AIO.

You would have to jump all the way to DDR5 8000 to see that big of a gain in anything. (and most games still wouldn’t be that much)

Not worth it unless you just want the best possible performance.

Yea, you don’t want to push modern games to just the p-cores. Here’s a pretty extreme example with Starfield that I found during testing. Check out the bottom result in the graph which is with e-cores disabled.

https://www.overclock.net/threads/overclocking-raptor-lake-refresh-14900k-14700k-14600k-etc-results-bins-and-discussion.1807439/page-246#post-29264559

I would go with whatever is on the motherboard QVL list. Might also cross check this against the motherboard list of the memory manufacturer if they have one.

I think generally you don’t want to go above 6400 with 64Gb due to stability issues. It varies depending on the mobo and quality of the CPU IMC.