I think more the processing power Apple had a pretty crappy bloated system. OS 9 crashed at least twice daily. Their towards the end it became increasingly unstable. Then came the first version of OS X, that really was not all that optimized in it's first incarnation. Once Panther OS X 10.3 came out things got a lot better and increasingly stable. The switch to Intel was a brilliant move that Apple had planned since they ported NeXT to the Power PC, but still developed  a secret version for the Intel architecture, as a brilliant plan "B" strategy, that apparently  is reaping huge benefits. The G5 was not a bad processor, but it was power hungry and ran hot .

I had the last of the Power G4 dual mirror door boxes, the wind-tunnel model. It was like working with a semi quiet blow dryer. I did get used to the noise, did not realize how annoying it was until I got my G5 that would on occasion  rev up those fans. But I though that was kind of cool sounding (on the G5, not the G4 that was incessant noise).

Now tomorrow I get the Mac Pro, from what I hear it is a very quiet setup so I am not to sure if I will miss the fans on the G5 :)