there is something called mean piston speed that is a limit for RPM and it really all comes down to stroke length.
They say fast stuff is like 20-25m/s (they being this wikipedia article that i read.)
Only REALLY fast motors (top fuel and F1 stuff) really move faster then ~25m/s.
from some real brief calculations, a puch spinning 12K is moving at 17.2 m/s. I'd say that's pretty badass.
anyways, heres the wiki link!