There's no real difference in size between the 13 and 15, just screen resolution. I use both sizes frequently, and I like my 13" more. The side bezel bothers me, and I don't wanna risk getting dirt/crumbs in the speakers, there's enough junk in my computer already.
I'd say, get the 13, from the apple store, for 1100 (student discount) and dont forget the free printer. WIth the rest of the money, get an SSD and just chill.
After you get the SSD set every program to run at startup and show everyone you know how fast that thing is.