Just my... "$0.02".
I was looking at some reviews of the 280/5s or something similar and they had a pretty good system for the rest of the test computer and it drew in about 350W - in total!
I think it was with a quad core CPU, 4GB of RAM and a high-end motherboard... something..
That's similar to the stuff I saw. QX9770 CPU, 4GB RAM, Asus Striker II Extreme.