BVH wrote:1. I'm wondering if I can get higher Amp controller that will work with these motors - Mxus or other brand. Max dimensions are: 2.5" wide, 4.25" long and 1.5" tall
Any sensorless-capable controller that meets your voltage and current and volume requirements ought to work on any typical hubmotor.
I don't know of much in that small a size, though.
2. Where can I find the specs on max Watts for the motors?
There probably are no *true* specs for them, unless JustinLE or others have done testing and measurement on them. There are some recent threads about such testing on some motors. I wouldn't count on anything the vendors say about them.
3. Is the difference in top speed in my two motors just a different type of winding or is there some circuitry inside them?
Probably just the winding--otherwise it would be a change in the wheel size attached to them, or the controller's speed limit or voltage applied to the motor. There's not really much you can put into the motor directly to speed it up.
Keep in mind that a more powerful controller will also apply more heat to the motor during startups, acceleration, and hills. If it's a geared motor that extra heat could cause problems (poke around the forums for many threads and posts about that).
Also, whether that will get you to the speed you are after depends on the motor wind and wheel size and battery voltage, too. If the wheel doesn't spin off-ground at least 20% or so faster than the top speed you need out of it, it probably won't do what you want regardless of controller, without higher voltage as well. (assuming there is no speed limiting in the controller).