You could try the LRP Sphere and X11 13.5t motor.
If you opt for the standard Sphere this has a 5.5t limit, although I'd probably still recommend getting the heatsink kit for it if you think of running the 7.5t or 6.5t motors.
You've always got the Nosram version of these too
www.lrp-electronic.de
www.nosram.com