Hello. I've been using an old samsung laptop for about four years and it's time for an upgrade. I need a laptop that will last for a while, and it needs to be smallish so I have decided on the 13". My main uses are: A LOT of excel spreadsheets, the computer has to handle these fine. I use XCODE often as well as Canopy so it must run those well. I do a lot of numerical programming on both xcode and Canopy with python so it has to be able to run scripts pretty fast. I will also dual boot windows, and use VM for linux. I have narrowed it down to this: Macbook Pro retina 13" - 2015: 2.9GHz Dual-core Intel Core i5, Turbo Boost up to 3.3GHz 16GB 1866MHz LPDDR3 SDRAM 512GB PCIe-based Flash Storage Intel Iris Graphics 6100 Force Touch trackpad Now I'm having second thoughts, should I upgrade the CPU to the 3.1GHz Dual-core Intel Core i7, Turbo Boost up to 3.4GHz ? I've done some research and it seems as though both CPU's use hyperthreading and that the main difference is the 0.2 ghz in speed, and the 4mb L3 Cache rather than the 3MB L3 cache. I don't know if there are any other differences, or how these differences will affect me. I won't be gaming, it will mainly be used for programming but please note that I will have two 1080p monitors hooked up to the machine, and it HAS to be able to run the scripts I throw at it smoothly. I'm also interested at the resale value of the computer. In 4-5 years I will probably sell it and upgrade, would the i7 be better for that then? I understand that the 15" seems to be more down my alley, but I really like the portability of the 13". Any help please! Thank you very much.