So after checking the motherboard, cpu seating, cooler seating, RAM, adding a fan to northbridge/VRMs, checking all my cabling to make sure there are no shorts and reseating GPUs & RAM i am still experiencing shut offs.
My only guess now is that it's the PSU, it only seems to do it when i overclock and take the voltage above about 1.4v. Again it's totally random and i have cool n' quiet on so it is throttling under low load. Sadly my PSU is not from OCUK but from the Bolton based retailer, should i RMA it and get a replacement? My only worry is that they won't find it faulty as it technically works, just seems to have issues with higher voltages.