maybe the patch will change things, but as it is, you want as much videoram as possible. SLI/xfire doesnt double your available vram (textures are duplicated on each card), so that is not the way to go -even if a future patch will enable it, for now it doesnt even work.
The best somewhat affordable solution is probably a 2GB ATI card, but I share your concern about drivers. If you can afford it, a 3GB 580 GTX would be your best bet. One of these:
http://www.overclockers.co.uk/showpr...14&subcat=1812
Pricey, but people are reporting excellent results, even London map being smooth.