I wanted to inject my experiences as I have a 5900x CPU paired with a rx 6800. I upgraded from the rx 5700 xt and I am very happy with the rx 6800 performance. Very smooth at 4k with HDR turned on and ultra settings (T-LOD at 200) and locked at 40fps - a real breathtaking picture on my 55in QLED TV! I also use FSR2 which works very well - the only issue I have noticed is slight ghosting around the wheels when taxiing which does not bother me. The rx 6800 GPU is at 50-95% utilization and my 5900x is at 25-35% utilization (GPU 90-100% with FSR2 turned off). I am GPU limited under 2000ft and at larger airports and CPU limited at greater than 5000ft - what I consider to be the perfect balance for MSFS.
A couple of things to consider are
- GPU VRAM - more equals better performance on MSFS (the 6800 has 16gig VRAM)
- Power supply - the rx 6800 recommended PS is min 650watts whereas the rx 6800xt is min 750 watts.
- Make sure the dimensions of whatever video card you get will fit in your case.