I have the gigabyte z68-ud7-b3 motherboard which supports x16/x16 sli but i cant seem to get it to run that. I have 2 GTX 580's which are both installed into the correct slots (PCIEX16_1, PCIEX16_2).
Nvidia control panel says: "For optimal 3D performance, plug the GeForce GTX 580 (1) into a high performance PCIe slot."
and the system information in the control panel lists the Bus as PCI Express x8 Gen2 for both of the cards.
When i disable sli mode i still get the same result. I am currently running MB bios F7d. I have tried reseating the cards and doing a clean reinstall of the drivers. I also tried calling gigabyte to see if they could help but i spoke to an idiot asian woman who concluded that the only way to fix it was to flash a newer bios on both my cards.