I know that normally 2GB vs 1GB renders no change in performance, but I plan on doing eyefinity across 3 23" displays and therefore I feel like the extra RAM will be handy for this larger resolution.
You want the 2gb cards for eyefinity. Mixing even one 1gb card will limit the other two cards to using only 1gb each. So do your setup with 2gb cards for eyefinity. It'll be much better.