I think there must be a lot of swap, I can definitely hear the disk spinning. Plus it takes forever to save big files (~300mb and up).
Though it's true that there is also quite a bit of general unresponsiveness when working on those files, which could also be due to cpu.
However, in both cases I would get 8gb (now 4), so the ram would not be a difference between the two options. If cpu and gpu aren't that relevant I might as well get the air.