Obviously the 13" MBA would be able to handle these things a bit better with the faster processor. The 4 gig upgrade would be an obvious choice as well.
There are some mixed reports on the 11.6" and playback of 1080p video. Converting to 720p if you can wouldn't be a bad idea for either the 11.6" or the 13" models, as space is obviously limited and they don't have 1080p res screens anyway.
Overall though if you're not doing this sort of thing all day long, the MBA shouldn't let you down.