RC motor build?

So I got my Giant LaFree with my RC motor running. The motor will run on anywhere from 4S to 10S, what should I be shooting for? At a lower voltage, I figure it will pull more amps. Is there a sweet spot for these RC motors? The motor is a 200KV, 3,000 watt motor. At real low RPM's this thing has tons of torque, pulled the bike out from under me, till I got the speed control turned off. This was a test at 4S.