I am a Windows guy and trying to make the switch to Ubuntu. On my desktop PC with high end specs, Ubuntu runs fine with only 1 RX470 plugged in with a riser.

When I plug in the second RX470 with a riser, the GUI of Ubuntu runs painfully slow. I have tried the AMDGPU-PRO drivers and the ones that come with Ubuntu clean install with no results.

Does anyone know why running 2 GPU's on risers causes Ubuntu to lag while running only 1 GPU with a riser runs fine?