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The current is proportional to the torque and the speed is proportional to the voltage. So how the motor reacts depends on how it is loaded. The current of the motor isnt from the rpm its from the torque, but the increased voltage allows for increased current to flow (ohms law more or less). All this is going through a throttle control, depending on the motor and controller type (likely brushed dc), so if you have 18v going to the controller (which may fry it btw) at part throttle you can have substantially less at the motor.

However under full throttle full load if you double the voltage to the motor you will double the current and ~quadruple the power. You are also accelerating at 2x baseline by conservation of energy. Nominally at least, in reality it is worse because the motor is outside of spec and loses efficiency and basically turns into a heater.

320 watt rating is a completely nominal rating for the motor based on the company's confidence in it to produce power without blowing up. IF you put 100vdc into it and run it into a stall it will dissipate a few kilowatts as heat for a few seconds before it burns out.

Not trying to be argumentative on this, but backing out current from the power rating is the result of a fundamental missunderstanding of how motors work.