Luis,
I would first like to say that I am truly unbiased as far as Mac vs. PC's.
Right now I am on a 2.4Gig P4 with a gig of DDR333 and this thing will run like hell. I can practically run packets of SETI as fast as they can send them to me.
The answer though is plain and simple, it's the Mac. Music proccessing is of serial nature generally. The data proccessing flow is under tight scrutiny. This is where the Mac shines really strong because that is more so how it works than a PC. All the apps you mentioned will run better in Mac's lower level language (Mac software verses PC software)
Macs cost a fortune compared to PC's. It is very hard to find great deals on Mac G4 1Gig Powerbooks, but they are out there. You have to snag it as soon as you see it. Good luck sir.