This may be perfect with those tires.........its a 550 and its stock in the HPI Brama buggy.............
http://www3.towerhobbies.com/cgi-bin...?&I=LXWYE2&P=7
This is one i run for torque applications and big tires............its a great motor, it will suprise you with the speed with those tires.
http://www3.towerhobbies.com/cgi-bin...?&I=LXTRC0&P=7