Hi,
if you are still interested, I had witcher 3 running without steam vr. The game is very performance intense with vorpx. I have a similiar PC. Try lowering the resolution to 1600×900 and lower settings in witcher to see if it is better. Higher resolutions were choppy for me, too.
1. launch vorpx
2. launch witcher 3
3. set vorpx cinema mode without the head controlling the mouse movement
regards