Which Powerbook? Please Help!, ...with general CPU usage questions... Options

[Esharpest]

Hello all (from a virgin poster)...

It's time for me to upgrade from my old vintage 1998 Beige G3 minitower (running at a whopping 233 MHz). I've been saying for a while now that when I do get a new computer, I'll finally be able to get into digital audio. At the moment I'm not working professionally in music, but am hoping to get back into it, and have recently made some baby steps with some live (classical) recording work for others, and a few collaborations with local producers as a session player on keys.

I'm currently torn between the 12" 1GHz PowerBook and the 15" 1.25GHz PowerBook, along with a USB or FireWire interface of some sort (isn't it a shame that the new Lexicon and Mackie interfaces come with PC-only bundles?). I'm going to need to be able to record several live tracks, edit and master etc. with something like Logic or Cubase; but I'd also like to experiment with production of entire tracks using virtual instruments. So - will the 12" be enough for self-contained music production? Or will I find myself soon wishing that I'd bought the 15" for its extra 250MHz of speed, the faster video card, and the bigger screen? (I'll keep my old 17" monitor, so when I'm at home I can have dual displays running.)

Any other suggestions?

Thanks for your help....