@itix
As long as the morphos devs have full access to the hardware details, then once MorphOs has reached a mature state on the 460, then I suspect we'll find there's very little difference. Of course before that state is true, then yes, MorphOS may well appear slower and that wouldn't be a fair comparison either. Look at G5 benchmarks on MorphOS now compared to their first beta releases, there's quite a difference.
@everblue
There was a link above to an OSnews article that compared non-optimal beta version of OS 4.1 on a Pegasos II with a mature MorphOS version and said "oh look! Morphos is faster, therefore it is better".
To make a true comparison (as if that would help anybody), you need to compare a fully open hardware platform running mature versions of both of the OSes.