So I think it's time to upgrade from my early 2008 15" MBP and I'm considering the following: Either the base 13" or the base 15". Considering the large price difference I need to justify what I'm buying - I mainly do alot of email and internet PLUS some pretty heavy Photoshop. The portablity of the 13" seems very attractive to me (I do photography) but the screen size concerns me as well as the shared video memory. What to do ??