An electric motor will draw maximum amperage at zero rpm and minimum at redline. The harder you want the motor to work will be the deciding factor. It you are trying to lift a cinder block off the ground, you will burn the motor out. Thats why we have gearing. It take the load off the motor but you have to sacufice something. That something it time or distance. It will take longer when you have your gear ration higher.

For example:
A 2:1 ratio means for every 2 times the motor spins, the output shaft of the other gear will spin once. It takes half the load off the motor but takes 2 full revolutions to accomplish the same distance or twice the time.

What is your "load" and what are you trying to accomplish. If you are running a propellor you will be fine. If you are trying to lift a brick, you may need some sort of reduction gearing to help.