Use 50 fps, that's a perfect value.
I'd say 30's fine, 50 seems pretty extreme...
Anyway, I agree that it can be annoying if you have a couple arbitrary seconds of lag, so i think we should probably double the amount of time FPS needs to be below 30 before recs get deactivated. And more importantly (said this to moo earlier actually) i think the record deactivation thing should only kick in maybe 20 seconds into the race; it's always laggier at the start when there's a huge clusterfuck of people racing, especially when cars first spawn. The feature's a good idea, but I think at the minute it's a little TOO sensitive and it's doing more harm than good