What AA you on in Pcars now?
I think I'm using the lowest AA setting right now. PCars is extremely demanding, and even the GTX1080 is struggling. So I use low settings in general. But without reprojection, at native 90Hz the image appears to be a lot clearer!
I turned off reprojection, turned on the frame drop notification in the Steam VR settings, and then tried different tracks, visuals, number of cars etc. It's hard to find the best scenario, because you need to restart the game for every graphic tweak, and every track has "that spot" which provokes framedrops.. Spa is impossible!
Oh, and a tip for everyone; PCars look extremely overexposed/washed out in the Vive at times. But go to the "Exposure Compensation" in the visuals setting and turn it down to "70" or something, that'll fix it.
After testing I found out that reprojection/timewarp is even worse than I imagined.. It kills IQ and steal presence. A little bit of async timewarp would help as a band aid for some light drops, but believe that developers is key to smooth out the difference between the highs and lows to ensure a somewhat stable power curve at native framerate.