I'm buying either the 13" or 15" (with dedicated GPU) rMBP and I can't decide on which to get. The size of the 13" is perfect but I notice that something like having a lot of chrome tabs open slows things down a bit so if I connect a 4k Monitor to it I feel like even the new 2015 version will perform the same. I also love to take photographs, and my 24 Megapixels raw files are hard to work with in lightroom so when I upgrade my camera to 42MegaPixels I will have more issues I would think so I'm leaning towards the 15".. I just dont like the size of it so my questions are: Is a maxed out 15" with dedicated GPU that much more powerful than the maxed out 13"? In what way will the deidcated GPU help? Can this help free up RAM being used? How is traveling with a 15"? how is the fit on airplane trays? Any thoughtsfrom anyone that upgraded from a 13" MBP to a 15" MBP?