The HS5245 has the perfect size/weight/power for bashing but for racing, I've been using the HS81MG for a few years now. Its all about leverage

I am also ONLY using rear brakes. You still get some front braking power from the center diff but not much (depends on how heavy the diff fluid is)
I also picked up a Electrik-Clutch adapter. What type of clutch shoes and springs are you using?
I plan to run without the clutch springs so that the shoes will engage sooner.