I have a Vega 64 and there are performance issues. For example in IL2 Battle of Stalingrad I was getting ~60 FPS on my Odyssey HMD.
Exact same setting in the Pimax is giving me ~20 FPS. So while performance would be expected to drop it should not be that drastic.
2560x1440 x2 - Pimax 5K+ pixels: 7,372,800
1440x1600 x2 - Odyssey pixels: 4,608,000
So I would expect ~40% performance hit, not 66%. I am messing with settings to see what I can get as playable and will post my results in a separate thread. Might help provide some expectations and insight for AMD GPU owners.