I am also about to get a MacBook Pro for editing with fcp 7. Does the 13.3 or 15.4 size make a difference?.
You realize it's pointless to get a new MBP for use with FCP 7, right? It's an outdated 32-bit program, so it won't be able to take advantage of any of the extra RAM or processing power of the newer i7 architecture. Go FCP X or Premiere.