> Showgirls (not much bandwidth required)is faster on my powerbook

This may very well be a case of ShowCase (the politically correct name of that application since MorphOS 3.10 ;-) being compiled for G4 or earlier. I wonder how this comparison would pan out with a G5-specific executable. Or it may be a case of ShowCase making extensive use of AltiVec, which is usually faster per clock on G4.