Computer Freezing Under Heavy Load

My Build:

PCPartPicker part list / Price breakdown by merchant

The Problem:

Whenever I play graphic-intensive games (e.g. Sniper Elite 3, Dying Light, Grand Theft Auto 5, etc), my computer almost always freezes frame and becomes completely unresponsive. Sadly, no blue-screens or helpful error messages appear. I say "almost always freezes" because if it doesn't happen within ~3-20 minutes, it simply will not happen no matter how long or hard I stress it. After this crash has occurred, I can USUALLY reboot and relaunch the game to continue playing indefinitely. This vicious cycle starts over again after leaving my computer off overnight. I have not tested leaving it asleep/hibernating. Also, no freezing ever occurs with low to moderate graphic-intensive games like League of Legends. This problem started after I upgraded my motherboard, CPU, and RAM. All were installed at once due to compatibility issues with my old parts.

I Have Tried:

• Monitored temperatures: All temperature readings seem to be very safe at time of freeze (Never even come close to passing 75c on CPU or GPUs when not overclocked).
• Turned on/off various overclock settings on CPU. Right now I have nothing overclocked.
• Down-clocked RAM to 2133 along with manually setting the timing/voltage as printed on the stick itself.
• Turned on/off XMP & OC Genie
• Removed one of my graphics cards entirely. This along with disabling SLI seemed to vastly improve my odds of not freezing, but it still happened. "SLI PLUS" my ass. I run 1440p so only using 1 card when I own 2 is absolutely unacceptable.
• Ran off each stick of RAM individually along with running memtest86 on both
• Completely reinstalled Windows 7 OS
• Updated BIOS to latest version (v1.9 from v1.8)
• Hooked computer up to wattage meter. At its absolute worse in stress-tests I just barely passed 600w with no issues. However, this is an unrealistic scenario. Most gaming never took me past 450w and I've even watched it freeze at 250w.
• Moved my RAM sticks to DIMM 1 & DIMM 5 as instructed by my mobo's manual. I believe they were originally in DIMM 1 & DIMM 3 because the print on the board itself implied that should be the case.
• Installed some "important Windows 7 updates".
• Used MSI's Live Update to get all available drivers for motherboard.
• Reseated all the power cables I could find.
• Messed with the "Power Saving Options" settings.
• Uninstalled RealTek audio software (Someone said it worked for them).

Some Thoughts:

I believe the problem to be the x99 motherboard. I've found a handful of people having this issue who are all on the same or similar x99 boards (even not on SLI or Win7). Maybe it's incompatible with the RAM or other hardware I have? Maybe it's faulty and needs an RMA? I would really like to figure out exactly what it is before I go paying to ship back a working board, decommissioning my PC for a week, and then ending up not fixing it.