one comp. is a bad idea. you always need a backup. Esp. if it is for your work. Break/ send one out for repair and your screwed
He could keep the old MBP for that purpose.
I am keeping my old crap Windows laptop around for exactly that reason. In a pinch, I can get my working environment up and running on that thing in about a day.
I have backups, naturally. Need backups because HD failure is not a question of if, but rather of when.
Anyway - I have a 17 UMBP as my primary working machine. I have a 24" 1920x external monitor which I never use - the built in display of the MBP is good enough and I am so used to it by now. The 17" with the long battery life is really a fantastic machine.
My older 15" MBP had severe heat issues - the 17 has none - it's perfectly fine, might sometimes get warm, but overall no problems. That, in turn, improves reliability significantly. I am convinced that I had so many hard drive failures in the last few years mainly because the drive got too hot.
Edit: And yes, I am getting the 1TB drive. I am thinking about actually putting it in the optibay (see another thread here), and installing a fast 120GB SSD as the main drive. Speed of an SSD, room of a HD - best of both worlds.