PSA: 9800X3D is the ULTIMATE CPU for Kerbal
I don't have any before & after screenshots, but I recently upgraded from a i5 12600K to 9800X3D. I posted here asking if this would give me good performance benefits for Kerbal. Most replies said it wouldn't be too much of an upgrade since KSP still will just use one core and I should just stick with my i5 12600K. It seems like the 3dcache helps a ton though.
The performance gains are insane. A craft I used to get 20fps with I'm now getting a smooth 60 to 70. One of my minmus bases I used to get 30 fps with I now get 80.
This is with a fully modded graphics setup including parallax continued & volumetric clouds.
I saw a screenshot in the Kerbal Space Center of someone who also upgraded and went from 25 fps to 90 fps. That's mainly what pushed me to do the upgrade.
Just getting this out there for people who are considering upgrading, as when I was researching this I could find little information on how it performs with KSP.