I have a 4 card rig (2x 570 & 2x 580) with a bronze PSU that consumes ~580W at the wall. When the system is idling it consumes about 80W, so it's taking about 125W per card. With a more efficient power supply it could be 115W/card or less.

GPU-Z and afterburner report between 80 - 90 W each, but that only accounts for what the core uses and not efficiency losses or memory subsystem.

Those numbers are for mining ETH only though. I'm not sure what kind of load or voltage it takes to dual mine, but the last time I tried it (way back when Claymore first implemented it for DCR only) it was way too high. With ETH only the cards are running @ 850 - 925mV @ 1220MHz on the core.