The big gain of Poser 5 on the Mac IMHO was the stability gain. Whenever I'd set about rendering large scenes it would croke, or worse loose all the textures.

As far as the 3x faster issue I'm pretty sure that it comes down to how the G4 processor is designed. Classically Pentiums are thought of as being really good at dealing with integer calculations, PowerPCs chips are better at dealing with floating point numbers. Remember that the Altivec in G4's is a dedicated set of registers for dealing with floating point numbers, so if you feed the processor floating point calculations it can deal with them, essentially, in parallel with the other processor activies. The problem comes because there is no hardware means of converting a integer to a floating point number, so this needs to be implimented in the code. Because people don't think about processor differences sometimes, they forget that not actually optimizing the program for that processor (which is more than clicking on the optimize for G4 button in XCode) will result in it taking a serious performance hit.

Anyway, just my 2 cents, but I love P5 :-)