Electric Skateboard

Hi,
I have a G1 electric skateboard that I modified to 36v, I took off the board and added 10" put in 3 12v 12ah led acid batteries, a 36v 500w speed controller, but left in the 24v 200w motor, It works fine,goes 16 to 19 mph, My question is if I change the motor to a 600w 36v will I gain any speed? Or will I just gain torque, without changing gear ratio...
Thank-You,
Todd Owen