Soldato
185W for the 580 is definitely not sipping power.You would imagine they have found some power savings as they have upped the clocks and Oem designs are said to be running at over 1400 mhz. I would imagine to get there on 480's you would have to up the voltage a decent amount using way more power than AMD would want v a gtx1060 which sips power.
https://videocardz.com/68586/amd-launches-radeon-rx-500-series
That's more than a GTX 1080 isn't it?