Although pre-launch drivers of the GeForce GTX 680 let the GPU run in PCI-Express Gen 3.0 mode on Intel's Sandy Bridge-E HEDT (X79) platforms, the release drivers limited the GPU to PCI-Express Gen 2.0 on the platform. The issue carried on with GeForce GTX 670, and other graphics cards with "Kepler" family of GPUs. NVIDIA
cited reasons such as the platform not being PCI-Expres Gen 3.0 "certified" although it supports the 8 GT/s mode. The company assured users that it was working on getting its hardware to work on the Sandy Bridge-E HEDT platform in Gen 3.0 mode, and until it's absolutely certain about reliability, it is forcing PCI-Express Gen 2.0 mode.
NVIDIA released a patch that enables PCI-Express Gen 3.0 mode on Intel Sandy Bridge-E HEDT (X79) platforms, which lets graphics cards based on GeForce Kepler GPUs, such as GeForce GTX 680, GTX 670, etc., take advantage of 8 GT/s per lane system interface bandwidth. The mode could come particularly handy for graphics cards that are installed on electrical PCI-Express 3.0 x8 slots, as they could end up with bandwidth comparable to that of PCI-Express 2.0 x16. The patch should be installed along with the latest stable drivers. To enable the patch, run the executable and reboot the system. To undo the patch later, run the same executable with "-revert" argument in Command Prompt. Use only if stability is not absolutely paramount, or if the hardware is not operating in a mission-critical environment.
DOWNLOAD: NVIDIA GeForce Kepler PCIe 3.0 mode-enabling patch for Sandy Bridge-E systems
Source: NVIDIA