The new airs should definitely run them or apple will look very foolish since every shot of lion they use is on an air.
I was in you same boat i went with the low end 13" because i was able to up the ram to 8gb and the hard drive to 750gb since this will be replacing my early 09 imac. Unless you really need that processor oomph go for the base and upgrade the other areas like ram/hdd/or go with an ssd. mine should be here some time this week.