I am on the same question. I have the same setup as yours, and I’d like to know how much improvement can a 13900K have over the 12700k. Interesting to see ppl overclocking the 13900K to a stable 5.8GHz!
At the moment, I run FS2020 at 1440P ULTRA with the 3080, and I am CPU-bound with the 12700K OC to 5.1GHz.
I usually fly VFR with GA (no problem with FPS here, >= high 40s - 60s) but recently spending most flights with the Fenix A320 getting between 25 to 30 in large busy airports with traffic, and between 30-40’s up high.