My 2 door has 7 years and 120 races on the used Getrag. My 4 door has 1 25 hour and many 3 hour races with numerous different drivers on it's used Getrag also.

I think you'll be fine with the gearbox.

As for 4 door vs 2 door. My 4 door "felt" better on the track, but that might just have been because everything was new. I prefer the look of the two door, but would probably recommend you take the first good donar car that comes along.