Upload & Sell: Off
Actually the macbook air will be considerably slower for photography due to the video card. I have the 17 from 2009, the 11 mac Air and the 15" Retina. The two latter machines are run through a 27" thunderbolt monitor and I find the 11" (my favorite all around machine) really slows down in both Capture One and Aperture to the point that I would not really use it for any photo editing. The old 17 runs a bit faster in fact (upgraded to SSD drives)
The Retina is not upgradeable for memory (I bought mine with 16 gig for that reason) but the hard drive IS upgradeable.
btw, I also have a 13" which my daughter uses ... but I really wonder how anyone can edit with such low resolution. Anything is doable ... but the 13mba is a poor choice imho for the lousy 1440x900 resolution. You 17 screen is fantastic for that, don't underestimate the fact - because lugging a Macbook Air AND a 27" monitor ... really sucks!