Unstable N770 TF 2GD5/OC in "OC"mode - Help!

Hi Guys,
Using the MSI Gaming App which has three settings "OC Mode", "Gaming Mode" and "Silent Mode"
These three modes correspond to:-
1137MHz Core (Boost Clock:1189MHz) (OC mode)
1085MHz Core (Boost Clock:1137MHz) (Gaming mode)
1046MHz Core (Boost Clock:1085MHz) (Silent mode)
As listed on the product page http ://www.msi.com/product/vga/N770_...#hero-overview
The Gaming Mode and Silent mode all work just fine in "Heaven" benchmark, which as you know is pretty much the standard for stability testing now days. However when I put the card in OC Mode Heaven will freeze and lock the PC, after around 1~2 minutes - sometimes around then dragon scene or just after with the canons bit.
Temperature is not a problem as that is around or under 70°C.
Rest of my system :-
Gigabyte Z87X-OC (Latest F8 BIOS)
16Gb Corsair Vengeance LP DDR3 (fully memtested OK)
Intel I5 4670K Haswell - currently at stock for diag purposes - cooler with Corsair H80
Corsair TX750 PSU
Corsair Air 540 case
I'm guessing that the GPU is (for whatever reason) unable to sustain the high GPU clock in "OC Mode" and freezes/pauses the PC, obviously the card should be able to run at the speeds no problem as it's the cards spec.
So would this warrant a RMA or do you guys have any suggestions that may help?
A couple of videos showing the issue.
First up is "Gamer mode" -1085MHz Core (Boost Clock:1137MHz) - completes just fine.
Next is "OC Mode" - 1137MHz Core (Boost Clock:1189MHz) - as you can see, freezes, and I have to reset the PC.
Surely something isn't right lol
Thanks in advance


Test system stability apart from GPU running IntelBurn Test on maximum stress level for a couple of times. If runs without issues check temps of the vga under load using Afterburner OSD (>>How to use MSI Afterburner<<). Add the temps. Also try running the oc settings manually with Afterburner WITHOUT using Gaming APP and report results.