One more thing i like to add that i be using EyeFinity.Right now i get 45-55 fps on Xfx 5870XXX.With crossfire it will speedup the pc performance and at the same time i get 2gb..So i thought better to get good advice from you guys
For eyefinity, it's more about GPU power than how much memory you have. I use Eyefinity at 5760x1080 and I could use more GPU power. So crossfire. The only time I've seen 2GB to be needed is when you have 2560x1600 per monitor in eyefinity.