I think it depends on what you are doing. For example, my 800 Mhz iBook rips a cd about as fast as my 400 MHz G4, but for general use, the iBook seems faster (though it does have a QE compatible video card.) My iBook still only has 128 RAM in it too, so I would imagine things will get a little faster once I add some more. But that's just my 2 cents -- In this case, I would think the 400 G4 would be a good deal faster for Altivec stuff, but the G3 would be faster for non-Altivec (and snappier in OS 9)