[quote='Sarduci',index.php?page=Thread&postID=42038 #post42038]The third card is probably causing a bus bandwidth issue. I'm not sure of anything to test that other than looking at the your motherboard chipset and how much data your video cards put onto the bus vs bridge/chipset performance.[/quote]

[quote='Ozbert',index.php?page=Thread&postID=42317# post42317]You'll probably find that the second and third PCI Express slots on your motherboard are not x16 electrically.

I've got a board with three PCI Express x16 connectors, but they are electrical x16, x8 and x4. If I install two graphics cards in the x16 and x8 slots, they both run at x8.[/quote]

Interesting. My mobo is an EVGA [url='http://www.evga.com/products/moreInfo.asp?pn=122-CK-NF68-A1']nForce 680i SLI 775 A1[/url]. The manual claims, "Two full-bandwidth 16-lane PCI Express links ensure maximum graphics performance for next-generation GPUs and games. This feature offers twice the PCI Express bandwidth of x8 SLI solutions." So it makes sense that the 3rd card was a disaster.

I still get some degredation in perf from the 2nd card. I actually do better if I run monitor 2 (clones 2 and 3) off the same GTX as my main monitor, although it starts to run a little hot (81C today). I've played around with a 2 computer setup using Octopus and an old P4. I may eventually have to bite the bullet give up on single physical boxing. /cry