dual SLI-enabled Quadro GPUs is a good thing if you can afford it of course. Im not 100% sure but i don't think you can link 3 Quadro cards together.
I would think two will do you just fine though. I know more than a few people in here that would give there right arm for two hi-end Quadro's 
Dave 
From a readers' Q and A column in TV GUIDE: "If we get involved in a nuclear war, would the electromagnetic pulses from exploding bombs damage my videotapes?"