The current through a motor is solely determined by the torque the motor produces. Current and torque are related by the torque constant of the motor. The constant current operation of a DC motor produces constant output torque regardless of speed.
Power is the product of speed and torque.
The maximum power of a DC motor is produced at the operating point which is defined by operation at half the no-load speed and half the stall torque. Seldom will a motor be operated at maximum output due to thermal considerations. This is also the motor's most efficient area of operation. For use with gearing, the motor should be selected for the minimum speed practical by choosing a motor with higher voltage ratings than the available voltage supply. This will result in lower noise generation and better life characteristics.