I run a Fantom 21.5 Works motor. Still messing with the right gearing for it because it pulls like a freight train. Not a super high RPM screamer, but it has TONS of power and runs really cool (ran the main with 91 degree air and 114 track temp and it came off at 124 degrees).
I run their 25.5 in my F1 and I will tell you that I've caught Reedy's with half a straight lead.