First time I have seen this thread, and it immediately reminded me of the wake from Sleep issue commonly seen on Intel P67 chipset boards, and other 6 series chipset boards. How is that related to X79? Simply because socket 2011 CPUs at this time are Sandy Bridge architecture CPUs, not Ivy Bridge, and the X79 chipset is related to the other Intel 6 series chipsets, not the other Intel 7 series chipsets.

Your symptoms sound identical to mine, the PC starts when first started out of Sleep, or seems to. No video becomes active, although all the PCs fans are running. OS drive activity was questionable. A forced shutdown and restart would in some cases bring up a login screen, and a resumption of the desktop as normally seen on a wake from Sleep.

I have an ASUS P67 board, from early-mid 2011, that cannot wake from Sleep successfully, with a few exceptions. Short term Sleep's of less than ~1/2 hour can work, but that is not very useful. To this day no BIOS/UEFI or other fix has been found. Some users of my P67 board reported that Sleep did work.

The suggested fixes were disabling PLL Overvoltage in the BIOS, which did not work for me. Another was setting a positive CPU offset voltage. The strangest one was the claim that the temperature of the PC when woke from Sleep mattered, if it was warmer, it worked. IMO, that just indicated the level of desperation trying to debug this issue.

One of the best clues found involved the power supply being used. It seemed that cheaper, low end PSs worked better than high end models. The theory was the time it took for the PS's "Power Good" signal to the board was out of spec, being to slow. I found Windows Event Log entries that seemed to back up this notion, they said a device did not respond within a specified period. As I recall, it was over 500 milliseconds.

I also found an Intel document not meant for the public that discussed an issue with the 6 series chipsets (not the SATA failure issue), but of course I can't find it now, it's on a back up drive. Not that it had a fix.

This is the first time I've heard about this issue with X79 boards, interesting, but I do feel your pain...