Nvidia release a patch for GT 600 series VGA card to support Gen 3.0 speed on X79 chipset.
For detail information, please go to the link below.
http://nvidia.custhelp.com/app/answers/detail/a_id/3135/kw/600
Or download the patch file directly from this link.
nvidia.custhelp.com/ci/fattach/get/105062/0/filename/force-enable-gen3.exe
Please reboot the system after patch file installation, then the patch will start to work.
