I wouldn't back off on the OC just yet. It's pretty modest. The first thing I'd check is the vCORE. With it set to "default" both EIST and C1E will mess around with it possibly causing a crash under rapidly fluctuating conditions. I'd set it to 1 notch above whatever the default actually is. This will keep the voltage constant but still let the power saving features lower the multiplier during idle conditions.

Also look at your memory voltage. It's overclocked a good amount so an extra notch in vDIMM might also help. Try the processor first though.

For a test suite, I usually run memtest test 7 for 1 pass just as a first check. You can run test 7 without going through the others by pressing C,1,3,7 once memtest has started. After that, I boot and run prime95 with the Small FFT settings for 30 minutes. This stresses your CPU without stressing the memory much at all. If this fails, then you know it's probably processor related. When that's completed, run "custom" and make sure that the "memory to use" is less than the free memory. If you let it default you'll probably get lots of paging which defeats the purpose of the test. I usually let this run overnight.