Upgraded to 21H2 and latest nvidia drivers, HAG on it was ok, got a bit more fps but that’s mainly due to Nvidia CPL being reset with VR pre-render back to 1 and Vsync off. Smoothness was on par or just slightly worst than previous version of windows and nvidia driver 457.3. BUT it killed performance of all my other games like AC and ACC (race sims).
So all in, not worth turning on HAGs and latest nvidia driver. Went back to 457.3. Reset nvidia CPL to default and got same fps. But decided to set VR pre render to 2 for slightly better smoothness overall.
System: 5600x, 32gb ram, 3080, 1tb nvme, reverb G2