I used to use the last generation of Nvidia dual GPU cards the 285GTX. It was a combination of 2 x 375GTXs and if you look into the Tomshardware tests, it performed worse than a single 275GTX in WoW. WoW does not handle SLI well at all. If you are running multiple monitors then it may be worthwhile because you can run one monitor off each card using Isboxer. If you are running a single monitor then just get the GTX580 now. This is what I am using on a 30" screen and it is brilliant.