I've had "Circuit Detail" and "Texture Detail" on rFactor2 up to FULL with an nVidia GTX660 for some time now and expected I was getting the best track detail. I had "Wind and Crowd Motion" at MEDIUM or less, considering it unessential. I thought "Special Effects" was in the same category and had it at MEDIUM. Playing around, I just set "Special Effects" from MEDIUM to FULL. The first two tracks I tried afterwards, Le Mans and Monte Carlo, are a *different* experience, with no noticeable FPS hit (guessing it depends on available VRAM). Many may already know this - for those that don't, enjoy!
Brianza, Hockenheim, Portugal tracks - Wow! I've found this also improves some vehicle interiors (i.e. Eve F1, BES F430).