Hi everyone! I'm still undecided whether i should get a 13 or a 15 inch rMBP. I'd get the mid-range 13" with a few upgrades (2.6 i5, 16GB RAM) for 1609, or the base 15" (2.0 i7, 8GB RAM, Iris Pro) for 1785 (with Apple on Campus discount). Is there that much difference between the dual-core i5 and the quad-core i7 and between Iris and Iris Pro? Also, is the weight and size difference so noticeable when carrying it around? Consider that I'm planning to keep it for 4 or 5 years. Thanks in advance!