The AI doesn't actually drive the specific cars, as such, they're really just a cosmetic skin. It's better to look at which cars are being used by other human players who do well in the races you're in. There is an element of luck in whether or not you encounter one of the crazy fast AI. I think I did the Trial 6 times yesterday, and won 5 of the 6 times in race 2. A typical set of lap times for me was 1:35, 1:33, 1:32 sort of pace, reflecting being slowed down by other cars early on. That kind of pace won 5 of the 6 races. In the one I lost, my lap times were 1:33, 1:32, 1:32, i.e. I went unusually fast, yet there was a Cholla AI that finished about 5 seconds ahead of me, so it completed the race in something crazy like 10 seconds faster total time than the fastest AI in any of the other 5 races.