No time for a fully detailed answer Binos but everything you need is on the Apple site. The headline stuff you're bumping into is what pays for the site - as a site operator I can't see anything wrong with that.
If you click on the support tab you find hours of useful information there. You can look at the support forums for the iBook or the Powerbook models and you find links to the independent bulletin boards based on software very similar to PPRuNe.
As you're considering a 'switch' I put that word into the search engine and it came up with this particulary concise FAQ:
http://www.apple.com/switch/howto/
However, there is every possible level of information you could need with in the searchable knowledge base there.
Very quickly regarding processor speed: it's down to how the cycles and pipelines are used. As an example Walter Murch is an Oscar nominee for his editing of 'Cold Mountain'. The film was entirely edited on location in Romania using an off the shelf Mac with standard Apple consumer software.
I repeat: a standard Mac using ordinary consumer software a cut down version of which is delivered with every Mac.
The processor? A G4 just like in the notebooks. The processor speed? 1 GHz
Regards
rob