Freestrokes are generally just used as an exercise to eliminate unnecessary tenseness in your grip, not as a full-fledged playing technique, as they offer little control. Playing without using your fingers at all is just terribly inefficient doesn't allow very much control over the sick. My stroke comes mainly from the wrist, but the fingers still play a vital part is controlling the stick, especially at faster tempos. And like the previous poster said, there's no set "limit" for exactly how fast you could learn to play using any technique.