So I did some very (very) scientific input lag testing. Reading the forums people were suggesting either limiting the fps to 60 or 61 or using vsync. Other suggestion was to try to get above 120 or 200fps. My very very scientific method was to do burnouts with the ferrari 312. Less lag = less spins.
I did not notice any difference between 60fps or any other limits on or off. I tried 60fps with my current settings (I get at least 89fps in traffic (24 gt3 cars in imola on starting grid) and when driving alone I over 100fps easily). Felt no difference at all. Tried that with adding more graphics candy to bring the technically achievable upper fps limit closer to the 60fps limit. Felt no difference with the limit on. I was spinning out with full throttle launches.
Then I turned all graphics off and felt no difference with the limit on. Tried 60fps limit, then 61, then 72, then 133 and then 193. No difference. Then I turned the fps limit off. Felt maybe very little change with everything at lowest setting except aa and af both at 2. I get 229 with aa2 and af8 and 260 with aa2 and af2. If blindfolded I could not tell a difference between all those settings I tried. Well obviously not blindfolded, but you get my point. You may not see it or feel it but it is there because...
The strange is that despite me not feeling almost no differences at all I could control the burnout launches much easier when I was getting very high fps, like 260fps+. I could pretty reliably get full throttle launches (redlinining at 100% throttle and dropping it in 1st gear) and keep it under control. With either fps limited to any number or unlimited but lower fps it was practically impossible to get full throttle launches without spinning. I could literally not get one single launch without spinning.. Except when I was getting really high fps then it all became easy to get the launches without spinning. Same track, same car, same part of the track obviously.
When driving I felt no real difference, ffb was the same, car felt the same, lag felt the same but I could control the car better at high fps. The only difference I could really feel was the transitions from oversteer to neutral. When the rear starts to bite when coming out from powerslide or oversteer it was easier to control it.
Conclusion: Felt small difference and could control the car best with 260fps... Other settings had no effect. I'll try the vsync on next and I'd be really really surprised if with vsync I get best results...
The game doesn't even look that bad with everything off except some aa and af...