Since they have a $10,750.00 Quadro Plex SLi system for sale that you can pick Intel P4, Xeon or "higher" Processors or AMD Opteron format.
http://store.nvidia.com/servlet/Con...dia&id=ProductDetailsPage&productID=89884400# Check the Tech Specs tab on this page.
I'd say they support SLi on the Intel workstation chipsets.
That's a seperate box though, it's not like you're throwing two cards in a system and getting them to work. I have two FX4500s running on a 5000x based workstation, it works. But they use a riser with the nVidia switch chip that was also used in the 7900GX2. Theoretically, I've heard quadro's work in SLI on intel chipsets, haven't seen it done in practice though. I'll gladly test them on any of these boards as soon as I can decide on which one to get...