Originally Posted by Megol
In short MOVEP touches more critical spots than MOVEM. For a speed demon design this can be a huge problem.
They are both tricky to implement but the most important difference is how often they will be used. MOVEM needs to be as fast as possible because it would remain very important for any future 68k CPU. MOVEP is an ancient kludge which has very limited modern usefulness and can be slow. It is nice that Gunnar figured out a way to avoid trapping MOVEP but it was never a high priority. Now if MOVEM could move a pair of registers to and from memory each cycle then he has struck gold