my advise would be to continue to wait until the game is finished and then get a better idea at what its going to take to run it all maxed out. ( i wish i would have )
If you cant wait just to give you an idea the single card systems with 2G of Vram and over seem to be running well. The dual card systems with 2.5G Vram and over combined seem to work as good.
I can really only speak for my rig below which runs great (except for stutters) with everything maxed out as long as i keep it in 1776x1000 Resolution. as soon as I go up to 1920x1080 I get a slide show even with all the graphics turned down. (Crossfire issue maybe but still not sure until more patches come)
Good luck
cheers