I'm having trouble deciding between a rMBP 15" 2.6ghz i7 quad core retina or a new MBP 13" 3.1ghz i7 dual core retina. They're about the same price, and both have 8G RAM and 256 flash storage. The rMBP comes with a GPU (NVIDIA GeForce GT 650M with 1GB of GDDR5 memory) and the MBP (13") doesn't. I usually have the following things open (and am constantly flipping between them): MS word (with markups), MS excel, SPSS (several datasets) and/or R/Rstudio, preview, chrome (several tabs and windows), and MS powerpoint. I'd like to have this laptop for 5+ years. No real gaming, photo editing or video editing needs. Any advice on which is better suited to me? Thank you in advance!!