90hz vs 120hz

I was thinking about getting a new graphics card for VR, and one benefit would be a smoother refresh rate with my PSVR2. I've tried lowering the resolution in steam vr home and switching it to 120hz mod, but I can't see it. Before when I was trying to see it with my Pimax Crystal Light, the Pimax Performance viewer in the menu was switching between 60fps and 120fps. Basically I don't know how to tell if I am seeing 120hz because I want to know if it actually makes a difference.