I'm considering buying an 11" MacBook Air as a secondary computer. I'm a freelancer in the media production industry and have a maxed out 15" rMBP that I use in the office every day. I often need to do intensive video functions on that machine. I don't like to commute with that laptop every day and have been using a 7-year-old MacBook Pro (C2D) at home. That machine just died and I'm considering replacing it. From the base model 11" MacBook Air, which would make the biggest noticeable performance increase *upgrading from the i5 to the i7 CPU or upgrading from 4GB to 8GB of RAM? Every once in a while, I'll need to use the Air to watch uncompressed 1080p or even 4K footage, but won't be editing or transcoding on it.