I'm looking at the middle of the line 13 inch rMBP. I see it has 8GB of RAM and I plan on keeping this thing for 4-5 years. I make some movies in iMovie, listening to music, surf the web, watch movies, and do documents. Nothing really intensive, but it's between that for $1499 and the MBA for $1399. I know the Air has better battery life, but the rMBP has better resolution. Any advice?