Finny, I believe WPC systems drive the DMD at about 15fps (I think I read that somewhere).  The P-ROC's DMD timing is completely configurable, but we typically configure it to physically run at 60fps and feed it it frames at 30fps.  Regarding raw operating horsepower, a P-ROC based system is determined by the amount of horsepower in the PC you connect to it.  The software I'm running right now achieves a run-loop cycle rate of about 400 cycles per second.  All that's really necessary to process switch events in a timely matter (and to keep up with the DMD updates) is about 30fps. 

The stock WPC CPU runs at a fixed timing interval due to the 0-cross circuit; so you comparing apples to oranges.  The CPU operating speed doesn't matter too much.  Pinball code isn't very complex or demanding.  Of course, WPC systems use pre-drawn DMD animations.  If you want to fully render complex animations on your P-ROC-based DMD, you'll need more horsepower than a WPC CPU. ;)

- Gerry