I have a 2012 MBA 13", 4GB RAM, 128 GB SSD and the performance is outstandingly fast. The 2011 MBA is a slowpoke in comparison. The new core i5 and i7 chips are of the Ivy Bridge variety, so they car run faster with less power. The SSD has been upgraded to a faste variety and is now available up to 512 GB. The RAM speed has been upped from 1333 to 1600 and the video card is now the Intel 4000 unit. All in all, I think the 2012 is a great MBA, although the 2011 MBA was no sacker either.
Good luck with this unit.