For an R3 race car, the FXX is pretty common and effective especially on tight courses. Don't buy one because you get awarded it for some level (don't remember). For ones with long straights, people use the Viper or Veyrons.
I use a FXX and catch em in the turns.
I was test driving it on Road America and did some adjustments and broke 200mph in 5th gear. Did not have enough room to top off 6. Got to about 212 before I had to brake. Which is more then enough for an R3 class.