The idea for chain driven(or any variable gear ratio) systems is that your electric motor is at its most efficient and most powerful when its spinning at or near its max RPM for the voltage given. So with a geared system, you can achieve max efficiency all through from near zero to max speed. Im not sure but i think that the amount of time it takes to reach the same higher end speed as a non geared system is greater with a lower wattage regardless of gears. Basically the gears only help torque at low speed then the watts are the only thing that matters.