I've heard mostly all good things about the SS. Some people had problems with them out of the box. But with a new release from Novak that usually happens. They are supposed to have tons of torque, and the speed is comparable to a 12t. Just with longer run times, and a cooler motor, but a hot ESC, surprisingly.
It should work awsome in a XXX4, my only concern would be mounting space, the ESC isn't exactally small you know.