> From past experience with the Phase5 boards that had both 680x0 and
> PPC CPU's on them and the slow context switching that caused such a
> performance penalty, that as good (no, make that great) as those
> boards and software were and still are, they are no match for what
> has already replaced them.

You are probably aware of that, but just to make sure as your comment reads ambiguously to me:
Context switches are only involved when using the m68k CPU as the main CPU and the PPC as the coprocessor, such as done via WarpOS or PowerUP on OS3. When using the PPC as the main CPU (via MorphOS, OS4, Linux/PPC etc.), the m68k CPU only does the initial start-up of the machine and is then put to sleep (after all, in MorphOS/OS4 it's being emulated by Trance/Petunia), which means there are no context switches whatsoever involved when running a PPC OS on the PPC CPU of a combined PPC/m68k expansion board.