Why the fastest? I watch guys win 17.5 class win with the "slower motors" regularly. The fastest motor wont make you faster unless you have plateaued with a "slower motor". I like the Reedy Sonic which is in my sons stock buggy now but my lap times were the same with the Novak Ballistic which is supposed to be a bit slower. Maybe a better battery(or new) or different ESC designed for Spec class racing is what will help you more.