said by rwong48:
I've considered using the onboard or even a PCI/PCIE GeForce 8400GS for the 3rd/4th displays, but I'm not sure how they would affect performance of the primary adapter. Maybe I should try it for myself.
As a clarification, during gaming, the other displays will still be on, and have mostly idle material - as opposed to being disabled and re-enabled. The game itself spans only the primary display.
I run my primary display - a 30" at 2560x1600, off of a GTX260. I run left and right displays - landscaped 1280x1024 19"s, off of an old dual DVI 7600GS. Obviously I only play games on the primary monitor, but everything works perfectly. If performance on the primary is important, make sure only your primary monitor is connected to it, and run the other displays off of the second/third/fourth cards.
The triple head cards are nice if you want to game on all of the outputs. But given your stated needs, it would be a waste of money.