How long ago did you check? :P
Mid 2010 SLI has been pretty decent. Still not officially supported. Do a Timetest, SLI, DX11, Fullscreen -- solo or boxing. You will be surprised :)
WoW is 'partially coded' for SLI, but it is pretty terrible with DX9, scales quite well with DX11
I gained 22fps on my low, gained 35fps on my average and the high was just stupid.. 155fps increase.