the difference between motors
 

I have an 8xl now, and run it with IB 3200, if I get a 9xl, with the same controller and batteries, would there be a difference in speed or torque?

If you don't change the gearing, speed will decrease but acceleration will increase (assuming there's enough traction) since the 9XL is a slower motor.

Ok, so it I wanted more top end, I would get a 7xl, but I would loose some acceleration, is that true?

If you went with the 7XL, you should use a smaller pinion gear. The 7XL would allow you to go faster without necessarily sacrificing acceleration, but you would be sacrificing runtime.

The best way to get more speed is by using higher voltage. How many cells are you currently using?