540 they say no limit. Yes but as was stated by several people that statment was describing 2pole 540 motors.
The pro4 is very new and is a differnt animal. That speed control was designed before the release of the 4 pole Pro4. The pro4 draws power like a 1 to 2 turn 550 motor but in a 540 can.
Good luck. all I can say is you have been warned.
Maybe you could post your testing of this so others with the same question could search and find their answer?