So I got a second one of these cards and can't seem to get it working properly.
After about 2 minutes of mining the rig will shut off for 5 seconds, and then reboot. It seems like a power issue but I am using a 1500W PSU and have both cards separated with 2 powered riser cables. After some playing around I found I can get the rig running only under certain settings.
I can run any 2 of the GPUs at intensity 19, enabling a 3rd will cause the reboot.
I can run any 3 of the GPUs at intensity 13, enabling the 4th will cause the reboot.
I can run all 4 GPUs at intensity 8 but its pointless.

Can anyone offer any ideas as to what is causing this?
The motherboard i am using is an Asus P7P55 LX (8gb RAM). A bios update had no effect.