I have 5800X3D CPU and had a 6800XT GPU before getting a 4090. Once Asobo had ported the sim over to Xbox, the bugs that had previously been annoying using an AMD card disappeared and from then on, I was getting equal if not slightly better performance than people using a 3080. The only problem was that MR was basically unusable, which the OP doesn’t like anyway. I must also say, I really like the AMD Adrenalin all in one control panel software. I quite miss it now I’m back with team green.
I would say that a new AMD card could be very good value for money compared to a 4080 or 4090 and should perform really well in VR with MSFS. Best wait for some benchmarks first though, just to be sure.