I came across this awesome, technical read and thought I'd share it:

It covers the 601, up to and including the G4. I'm still searching for the G5 continuation of this article and will post it here if/when found. All pages for parts 1 & 2 are included in the PDF, but since this is the free version of the article (I'm not a subscriber to that site) the page numbers are not displayed correctly.

Part 1: http://arstechnica.com/old/content/2004/08/ppc-1.ars

Part 2: http://arstechnica.com/old/content/2004/10/ppc-2.ars/2