You're not alone in this. I've posted about the exact same problem. I've been playing BF4 on High Settings, and Crysis 3 at (5760x1080) on Very High settings with not a single shutdown or thermal event. I sit there and monitored my temps. I have also just ran "Extreme Fire Storm" in 3D Mark with not a glitch. I'm running a GeForce Titan, and the only game that completely shuts down my computer is Day Z. So it's not a thermal event or the PSU. I did notice that Day Z runs stable on "Rendering Resolution" of 50%, but once I up it to 100% it will always shut the computer down, usually at the main menu. I have had decent luck at 80% but it still crashes quite often. The only thing I can think of, somewhere in the graphic settings causes a crash.