I did something similar, but I went from a 12900K to a 13900K, and I was on a 3080Ti. I am not flying in VR. I definitely saw an FPS uplift, but nothing like 25%. Just generally snappier and more overhead available for complex scenery. I lock at 30FPS and I’m usually able to stay there even in London, NY etc. I rarely see stutters at all, although I do get the ‘microstutter every x seconds’ thing that some people have seen, but only at some airports (and not necessarily complex ones). This is due to a long frame and so far I haven’t been able to eliminate it.
Like most people, I find the key is adjusting settings to suit the load I’m putting on the sim. There’s no one size that fits all, even with the fastest CPUs and GPUs available. I’m happy I made the upgrade but it’s a lot of money for a relatively modest improvement.