Yup - idle wattage (with just 1 video card) is around 180-190W and with all 5 it is around 220-230. On full load it is 660-680 (depending on room temperature) -
So - my calculations say that it's 90-95W per card currently. (and I had to move them to another room that's not airconditioned so everything is running a bit hotter).
Can't even come in a neighborhood with the same settings... No idea why... One of the kill-a-watt is wrong. And based on 5850 specifications I believe it is yours. It is reported that it runs with about 150 watts on full. So undervolt and underclock of mem could save you 60 watts but you are overclocking GPU. So I don't think you can get it to save over 35% of the power that it is using stock. Is your kill-a-watt capable of detecting phase shift? EDIT: Sometimes this completely throws of this home meters.
EDIT: But it is a different design but still made by ATI.
Well - what I see roughly matches my electricity bill so I have no reason to suspect the kill-a-watt. And I am merely stating what I'm seeing.
By the way - undervoltaging the card does have a dramatic effect on power usage! Changes between 1.000 and 0.975 result in 10-15W on some of the cards. And downclocking the memory is important too as it results in noticeably less heat.