I have 4x Sapphire 100363L r9 280x doing 730 KH/s each on BAMT miner with the voltage modded to 1.050v, I measure the power draw and it was 990 to 1005 watts. 
I am using a 1200w PSU
I am using a 1200w PSUAre you counting only the GPU's? I bet you are, but I only want to make sure.
