Computer Reboot Issue

I recently built my first computer, and was enjoying a very pretty Skyrim when my computer unexpectedly restarted - no BSOD, no warning. No problem, probably just an unstable overclock or perhaps a really weird mod compatibility issue. So, I checked the Event Viewer, and nothing there. Odd, but not unheard of. I started Skyrim again, and the same thing happened. So, I uninstalled all my mods and started Skryim again. Again, it happened. It happened with or without an overclock (3.4 -> 3.7 GHz, nothing spectacular). I could not figure it out. This was annoying, but it only seemed to be happening in Skyrim, so I figured it was probably just a driver issue, since the 780 is fairly new. But then, it happened in Tomb Raider. And in Saints Row IV. And in Dishonored. And I noticed it happened during very specific actions. But here's where it gets weird. As an example, I noticed it happened about 15 seconds after entering Proudspire Manor in Skyrim - reproducible no matter what I did that day. But then, the next day, I could enter Proudspire Manor no problem and no crash. Then, it happened when I opened up the map. The next day? I could open up the map and fly around no problem. Same save, same mods, same everything except time. Even from a cold start, it would happen. Same deal with Tomb Raider and Saints Row. It would happen at very specific actions, but then not at some point in the future.

So I tested everything. Ran Furmark and Prime95 simultaneously and seperately for a few hours, no problem. No temperatures anywhere near abnormal (using OpenHardwareMonitor), no problems anywhere. Memtest86+ ran for quite a while no problem as well. Then I found that during the Unigine Valley benchmark I could cause it when adjusting the focus and aperture. Again repeatable. Then, the next week? I could adjust it and nothing would ever happen. Sometimes it will happen two minutes into a game after just turning on the computer. Sometimes it won't happen for five or six hours of gaming on weekends, only to crop up somewhere else entirely after the sixth hour.

So for the life of me, I can't figure out what could be wrong. Benchmarks run fine, except for Valley. Outerra never has a problem. No test I run ever turns up anything the slightest bit wrong, and there is never a crash dump. I have two ideas left. The first is drivers, but I have tried multiple versions (even beta versions) of the motherboard, gpu, audio, and chipset drivers. The second is that something running in the background conflicts at very specific times with very specific actions. (I have Rainmeter, PrecisionX (sometimes), and NVIDIA GeForce Experience running normally) I suppose I just need someone to tell me that Nvidia is bad at drivers and that I just have to wait a few months for them to get all the kinks worked out.

tl;dr: Random computer reboots during gaming, even though nothing seems to have a problem during testing.

The System:
Windows 8.1 64-bit
Intel Core i5-4670K
Corsair H100i Liquid CPU Cooler
Asus Z87-EXPERT ATX LGA1150 Motherboard
Corsair Dominator Platinum 16GB (2 x 8GB) DDR3-1866 Memory
EVGA GeForce GTX 780 ACX Video Card
Corsair Professional 1050W Semi-Modular ATX Power Supply

That would typically point to either severe overheating or a PSU issue to have full shutoffs without BSOD, driver crash, or lockup.

Normally, I would agree. However, all the temps stay *far* beneath levels that would cause reboots. And I would expect the computer to not reboot immediately if it shut down because of a heat issue. As for the PSU, I am fairly sure that it is okay, but I don't know of a way to test it extensively, and I don't have another I can swap out.

But just to confirm - yes, I get no driver crash messages, BSODs, or lockups. As I said, I am at a loss to explain it. Thank you for the ideas, though.