Yes CPU-Z stresses the memory until its all used up and the PC Crash's
This is why I had a theory of faulty RAM Also.
The CPU-Z, CPU Stress test will run and the benchmark numbers will drop from around 10000 - 11000 all the way to sub 1000 until the the PC Crash's.
However whilst this is ongoing, when monitoring the memory it seems to have less and less available throughout the test until there is non left.
Gaming with the OC off is fine I just get low FPS (Lower than in the past with the OC off also).
With the OC on I can game perfectly fine until I get a random crash, which can be either be 1 hour after playing, or days after. As there doesn't seem to be any trend to the crashing occurrence. To which it could happen 3 times in a row
Example;
PC Crash,
Restart,
Load Game,
Play 10 Mins,
Crash,
x3
or it could crash and not crash again for days.