My rig is too mediocre to really be a decent guideline for what most people would experience with an Oculus Rift but here we go. 2500K @ 4.5ghz, GTX 1060 with the latest drivers.
Laguna Seca, 22 car grid, day time, dry-rain-dry cycle: locked 45 FPS
Spa: 22 car grid, day to night cycle, clear weather: locked 45 FPS
Long Beach: 22 car grid, day to night cycle, thunderstorm: unplayable, sub 30 FPS at times
That's been my experience so far. I played Laguna on whatever the graphics settings defaulted to when I first booted the game and it looked pretty clean for a VR game but after the Long Beach test I lowered everything in an attempt to make it playable and it's pretty ugly in this state I must admit. I'm just trying to target 45 FPS, it actually feels fine surprisingly so I can deal with it.
Night driving in VR is pretty much a revelation btw. Just when I thought I was used to VR something new blows my mind.