I have a mac pro 5,1 running OS X 10.8.4. Recently tried using a GTX 680 non-EFI (PC version) and was running into numerous issues after about a week of use where the machine would not boot. Decided to return the card and get the EVGA GTX 680 Mac Version (with EFI/boot screens). Went back to the stock 5770 card in the meantime and there's no issues at all. Installed the GTX 680 Mac Version card last night, and as had the same exact issues as the PC version, but this time I could see what was happening... Machine was getting stuck at the grey Apple logo screen and the small rolling progress circle would "get stuck" right before it would load the log-in screen/desktop. I'm fully able to boot into recovery mode, select partitions, and run utilities with both keyboard (usb) & mouse (bluetooth) functionality. I have repaired permissions on the boot drive, but no changes after. Tried booting with my HDD clone and the same thing happens. Everything on the machine appears to be working. Swap in the stock 5770 card, everything works completely fine. Swap back the GTX 680 card, and it works fine the FIRST boot time only. After that, it gets stuck in this endless stuck on grey Apple screen. Installed the NVIDIA 313.01.02f01 driver - http://www.nvidia.com/object/macosx-313.01.02f01-driver.html and was working until shutdown/restart. Called EVGA and they said to call the retailer I purchased the card from and are offering to RMA the card. The retailer says call EVGA. I'd take it into Apple, but since it's technically a 3rd party card, I'm sure my support will be quite limited. The card appears to be "working" fine (as in outputting a display signal), and this looks like it's a driver or software related issue. Fairly sure this is not a defective card... have not run into this issue on any machines I've worked on recently with GTX cards. Has anyone ever experienced this issue with a GTX 680 card? Any recommendations before I try reinstalling OS X 10.8.4?