The 6990 is a dual GPU card, and has Crossfire enabled by default - it's subject to the limitations mentioned above (i.e. in Windowed mode games, only one of the GPU's will be active), so you'd be wasting money buying this card to multibox wow.

Here's a link explaining the limitations in case anyone is confused:
http://support.amd.com/us/kbarticles...lications.aspx

Cheers,
S.