Just picked up the 27in display today for the office. I was surprised how well the 11in MBA base model handled driving such a pixel-dense display. Although, I did get feel some noticeable lag when I tried scrolling quickly while image-heavy websites were loading.
http://farm5.static.flickr.com/4027/5130894180_65d95bc849_z.jpg
Great setup, pretty similiar to what I'm thinking of getting, just with the older 24in ACD.
What spec air is that and what websites were laggy?
iMac 27" i7 2.93 16GB 1TB Hard Drive