Hello. Im starting to do a programming in college this year, also I like to do some gaming. Im deciding between hi end imac 27 with i7 and gtx 775 or gtx 680mx (refurbished) + I thinking to buy mba 11 with 8gb ram for typing in college. Next choice is to buy mbpr top end, also I have a 27 inch 1080p external monitor. So the main question is how big difference is between imac and mpbr gpu?