I use mac laptops exclusively for live electronic music (using Ableton as a live DAW running various soft synths and hardware synths/drum machines and sequencers) it's not uncommon for my sets to have 8 channels of audio running at the same time with 20+ plugins running for live manipulation (including waves, and SSL plugins)
Until a few weeks ago I was running all of this off a 2.0ghz white macbook with 2 gigs of ram. It handled it all pretty ok, it wasn't at the limit of what was capable but it was getting there. I now have a 2.53ghz macbook pro with 4gb of ram and the thing flies! I can throw everything I can it and it handles it fine. The other issue was cooling/physical strength of the case. The MBP stays about 20 degrees c cooler than the MB, something that's very very useful in a sweaty club/venue! Also the plastic MB flimsiness was issue for me, laptops can get knocked or beer spilled on them and I think the MBP will handle that much better!
That being said I think the MB unibody or even the plastic one will be perfect for your needs. I used my plastic macbook to record live bands that ended up on MTV and channel 4 in the uk no problems. You could load up all you logic sessions with all your tracks and use it like a tape player. look into a program called onstage at
http://www.fluqe.com/
This will allow you to jump between logic sessions super fast. Or you could lay all the stereo bounces out at home and just play them at the show
WHATEVER you do DO NOT buy an Mbox. Digidesign make sh*t hardware (the preamps and A/D converters suck) invest in a good firewire interface (Such as the Focusrite Saffire/RME Fireface/MOTU traveller) you'll be thankful in the long run, plus you can use it at home. I also dislike pro tools, but that's for geeky technical reasons I won't go into here.
For your house maybe just get a big screen for your laptop?
Hope this helps.