Reply to retina macbooks- 13" or 15"?

I'm in the market for a new macbook. i know most people arent really on board with the retina macbooks, but i kind of want one (pure gearlust). the question is, should i get the 13" or 15"? they are roughly the same price with a student discount. the 15" seems too...big, but it has a discreet graphics card and the ssd space i need. the 13" seems to be a better size for me, but it lacks the quad core processor. would the processor even make a difference? i mostly want this for traktor/ableton and some basic photoshop work. any suggestions?