Just bought an i5 from PCAudioLabs with Win7 64bit pro , 8 gig ram. This config is a must for the future and Sonar IMO. Go for an i7 if you can afford it.
I use 500 meg eSata externals and firewire for FF800 . It will record 8 tracks no problem and many more. Look at their laptops and go from there. These guys are pro's so I recommend seeing what they are using or just avoid all the trouble and buy one from them. Their service long after your deal is made is exceptional.

I don't intend to sound like a fanboy but any 2010 MacBook Pro will work great for you. You might even be able to get away with recording to the internal drive, though I would get an ext FireWire ASAP. Keep in mind Thunderbolt is arriving on the scene.