Powerbook G4 Vs. Powermac G5, for hip-hop production Options

[Pig-Donkey]

I need some help with a looming purchase. I've been using a G4 Powerbook for about a year (800 MHZ), 15". The problem is that running some heavy audio programs causes the PB to be a bit sluggish at times. I am in season for a new computer and needed some assistance in deciding what I should do. Here are a few questions I have:

1) If I were to sell my current PB and by a newer 17" w/ 1.25 Ghz, would it be much faster? And does anyone have current experience using a faster PB and reccommend it for hip-hop production?

2) Let's say I decided to by a G5 Tower instead of a new PB, I would still keep my old PB and use it for portability. I love the idea of being able to transport my studio anywhere I want. Is it really worth spending around 2K more for the G5? If I didn't purchase the G5 I could spend more money on a hardware sampler like the MPC2000.

3) Can anyone give me some suggestions for a great production set up? I currently use GB and i'm ready to move to the bigger programs.

4) How much SDRAM would I want w/ a G5? Does it make much difference?

Thanks Much,
The Donk