Motors come in different sizes and versions. Different gearboxes requier different motor sizes.
There are Short, Medium and Large type motors. Next to that, you have High Torque and High Speed.
High Torque: High torque type motors deliver a lot of torque. These motors are usually more energy efficient, and provide a bit less wear. More torque means that you can pull stronger springs with more ease.
High Speed: High speed type motors have high revolutions per minute. Usually, these requier more energie. Due to the high RPM, high rate-of-fires are possible. These motors are less suited for strong springs.