Random lock ups during intense 3d games

Hi,

I have recently been having problems with my PC. I'm hoping someone here at Toms Hardware can help me out. Firstly here are my specs;

i7 960 @ 3.2GHz (stock)
Asus Rampage 3 extreme
x2 GTX 570 in SLI (also stock)
12gb Corsair Vengeance RAM (3x4gb)

My PC is locking up mid-game when playing 3d intensive titles like Battlefield 3 or Blacklight Retribution. Sometimes I play for 20 minutes, and sometimes longer before my PC locks up. In-game I usually start to notice a bit of lag, then I know its not long before my PC gets stuck mid-frame. Sometimes it gets stuck for about 20 seconds then resumes (I usually end the program via task manager at this point), and sometimes the whole thing will just crash and leave me with a black screen where I cannot do anything and I am forced to hard reset.

The reason I post this problem in the Motherboards and Memory section is because I am pretty sure that the GPU and CPU are not the problem, and I honestly cannot think what else could be causing this. I can also confirm that this is not a heat issue, here are my temperatures respectively;

GPU 1: 68 degrees Celsius (under 99% load)
GPU 2: 60 degrees Celsius (under 99% load)
CPU: 60 degrees Celsius (while playing intensive games)
Mobo: averaging in the early 40 degrees Celsius (while playing intensive games)


Temperatures measured with MSI afterburner and Asus PC probe 2.

My next step is to determine if RAM could be causing the issue, but Im having a hard time getting Memtest86 to run. Are these signs of RAM failure? If so, do I just manually remove one stick at a time to determine if the issue still persists?

Any other ideas as to what could be causing this would greatly be appreciated.

Thanks,
Gus.