i run an associated sc10 4x4 and can highly recomend the Novak Sc and thier 550 motor
http://www.teamnovak.com/products/es..._sc/index.html
i find it faster than a 10.5 540, though my 2wd has a 10.5 or 8.5 540 motor is it.
all down to cost and taste i guess