Doesn't NVidia Inspector cause the same lag as VSync? I don't know but somehow it amkes me think that any artificial limits would cause lagging.
I admit, using VSync is the final option and Race07 has always performed best with max settings. in 2008 era (that means 2005-2006 PC, i'm poor...) it was either low or max, anything in between didn't improve FPS one bit.. Now with 3 year old equipment it should be maxed. Checking background processes is a good thing to do, Race isn't optimized for multicore CPUs so it's more sensitive to background actions. I've had some antivirus applications interfere with race big time but that was some time ago, did a full round of av softwares recently (all 2013 free antiviral SW, MS Essential was the best, damnit..) and not counting updates or nagging screens, none of them caused any harm.
Oh and i have never had more than 12 cars visible, makes the most difference.
EDIT: Don't know if it counts but as a audio guy, the highest latency that you can "feel" is around 7ms on instictuous actions (playing an instrument is not really conscious, learning a new track is like learning a new song etc there are huge amount of parallels between the two). After that the action seems simultaneous. I would think the same goes for simulator and other games, make it around 3ms and i'll bet that no one can sense the difference.. 3ms is 333FPS, sound travels about 1m in that time..
We all know that playing something over 100FPS doesn't make any dfference, that getting really really close to that magical 7ms latency ( i remember reading somewhere that 120 is the human limit in theory, it was a lengthy piece with lots of fine words and graphs..). Allthou latency is always negative, it always adds to the reaction but the difference is really really minute if we are talking about input latency on a system that's controlled by a human.... My own experience tells that 30FPS is the lower limit, after that lap times begin to suffer. Spiky FPS is much worse so using VSync or some other limit is totally viable method. Input latency is secondary when it comes to consistency.