Viper asked me to put this here, I should mentioned that I have not been able to test this on my own PC, it's simply too weak to reach the framerate necessary to really "break" the game. But here it goes:

The game has a "performance loss catchup" feature where if the framerate drop is considered significant by the game it will give your car a little speed boost that almost instantly decays. So when it works as intended the average speed difference is way smaller than what's caused by human error, so no worries there. Until you go beyond 120fps, that is. In past tests I've participated in, dating to about 2 years back now I believe, it seems like the game overcorrects your speed if it's running faster than 120fps. So running the game faster than that and making it unstable in a particular way will fool the game into "correcting" you when it shouldnt, thus making you faster than intended. But on the other hand you dont want to bring the framerate down too far or else it will be percieved as more random. Because the physics tickrate is tied to the render framerate, anything relying on collision detection will be more accurate at higher fps.

You know about curb boosting, so imagine speeding over a pothole. Lets say the car skips past it at 30fps, but 60fps will just barely detect it and 120fps might detect it multiple times. It's like drawing a line the length of the distance covered in 1sec, then chopping it up to match the framerate. Each step on that line is one detection point. Naturally you'd want more accurate "scanning" of the road to increase the odds of consistent results, so cranking the framerate up as high as possible is desirable because of that.

It should be noted that I have seen the RE7B begin to self-boost beyond 140fps, so god knows what other cars break the rules beyond that.

• So it comes down to a balancing act of not tripping up the performance loss catchup thingy (decays too slow beyond 120fps according to older tests), hit detection accuracy (higher fps is desired) and spontaneous breakage (like the RE7B breaking the rules beyond 140fps)

EDIT: I'd suggest to settle on a framerate at or below 120fps, favoring some margin for error. A stable 110fps should make sure that the performance catchup doesnt trip up more than necessary, but 120fps could still work just fine.