fpsVR is the easiest way I've found to measure your performance in VR games, and at only $4 it's easily worth it.

It does what it says on the tin: it shows you your CPU/GPU utilization and more importantly, frame times.

I use it in VRChat to see if avatars are horribly unoptimized. I just toggle the avatar on and off and see if fpsVR shows my CPU or GPU explode when the avatar is visible.