Well, I was going to a grouchy asshole and say the motherboard wasn't important, but it is. Sorry, thank you.

If we're running multiple high powered graphics card power is going to be an issue. What is your Power supply rated at?

Seeing the motherboard, depending on your case, you could run three dual slot cards, or two tri-slot card if your case is large enough. For performance NVIDIA historically has lots of muscle, but they eat lots of power and piss lots of heat. ATI is innovative, with eyefinity you can run two cards, six displays. Unsure on where crossfire stands, but we want to power lots of displays.