Something to chew on....a boosted 13.5 or 17.5 may give the top speed of a lower turn mod motor BUT it will not have the required torque to clear some jumps with a very short "run up". Your needs depend on the track layout but a boosted stock motor is not exactly the same as a low turn (7.5-8.5) mod motor.

If new to 2wd buggy boosting a 17.5 at some point is a good option, it just doesn't have the exact same result.