The fuse is to protect the battery in the event of a short on the power cables etc.(and sometimes the controller if it is accidentally connected incorrectly), it is not supposed to to be used as a current limiter for the motor.
The maximum current available to the motor should be determined by the controller.
The Magic Pies can handle at least 100A in short bursts but I don't know what the maximum continuous current would be before the windings start to overheat.
Alan