Well as a drift car i find the FC chassis is more suited to slide, but the SA/FB can slide as well just takes a different style. Its all about driver skill so driver preference falls into that equasion as well.
To make a 12a fast there is not a hell of alot you can do. Different carb, intake and exhaust are basicly the bolt on parts you can get away with. Dual dizzy's will help with response but there is not alot you can do for little cash to make it fast.
But then again there not made to go balls out fast in a stright, there made to rip the corners apart and do the trick well