5 amps is a good place to start. To finetune it, get a Loadmaster from WMH racing. That will go with all your motors. You can then gear your motor for more speed, if needed. Watch your temps, though. Most guys will run temps up to about 160*F while some will tap out at 180*F. As you gear higher, you will also lose torque, so take that into consideration if you're racing in offroad.