BMS-630MG or BMS-660MG

Under super stressful conditions (or just for cool looks) the alum. case on the 660 will dissipate heat from the guts, most importantly the motor. Outside of rock crawling, I haven't heard much about people heating up their servos, turning the wheels while having forward momentum may be less than easy on them, but just doesn't carry the load of a heavy Clod or Maxx or TXT shifting all the weight to the rear axle on a steep incline........and telling the servo to kick the wheels to one side. Bashing may beat a servo to death too, but crawling has to be THE hardest form of rc on the electrical components.