Looking to upgrade my old MacBook Pro. I don't do a whole lot of video editing, but I dabble with iMovie and GarageBand from time to time. I don't have an external screen, and mostly work in Excel, MiniTab, and do other basic things (photos, movies, etc.) I'm debating between the refurb i5 15" MBP, or swinging by the Apple Store and picking up the low end 13" MBP (I have an education discount). Any input?