I would go with the 625. Since its an on-road car you want the throttle response to be fairly quick to get the snap out of corners. Also you won't need all the huge torque of the 645 for braking. Most of the time in On-road its partial throttle rolling through corners, not braking for stopping. Also if the throttle is too snappy for you, you can dial out some of the speed from the servo. But if the servo is slower to start with you can't speed it up. TTYL.


Gary F.