Hello, I'm purchasing a new laptop next week for college and I'm torn between these two. MBP 13", i7, 8gb RAM for 1399, upgrading to ssd would be 100-200. or MBA 11", i7, 8gb RAM for 1274, but I would also get external bruray for about 100 more. I need both to last at least 4 years...I like the upgradability of the MBP but also love the portability with the MBA. How big a difference is that 900mhz of processor? Any opinion would be welcomed, thanks!