I also just upgraded to a 5900x and a RX6800 (no xt though) so fairly similar and I get 55-65 fps w/HD10 and 60-70 w/SDR. I’ve got a Samsung 4K Qled TV as my monitor with a 120hz refresh rate. This is on all ultra settings Tlod at 200 and 2560x1440 (I let my tv upscale to 4k). I have a 650w Seasonic power supply which is the minimum for the RX6800 but I suspect you’d be getting some crashes etc if your power supply was not enough. I found turning off smt & svm in the bios to be very helpful in optimizing single core performance. You’ll also want to turn on PBO and smart memory access in your bios.
I would also make sure all default options are set in your driver. Edit: make sure your refresh rate is set to 165hz in Windows. Pic is at EGLL Heathrow runway 09R full ultra defaults DX11 no vsync with default A320. You can do a direct comparison on your PC.
