I’m running a 5800x3D and a 4080 and under certain situations can be main thread limited even at 4K. The 5800x3D and the 13900K are currently your two best CPU options for MSFS. There’s been some argument about which one is better but I don’t think that there’s enough of a difference to warrant an upgrade.
The new AMD non x3D parts are out performed by the 5800x3D in MSFS. Benchmarks show the new x3D parts do offer a performance advantage at 1080P, but I haven’t seen how much of a performance advantage that equates to at 1440/4K. I suspect there’s some uplift but that you will still find situations were the CPU is bottlenecking performance. You may move the bar up some but I doubt you will climate it.