are you talking about wattman? 80-90w? i know that rx470 will draw 130-150w on kawpow ofcourse if you want get 12-13mhs as soon as you undervolt too much you will get 10mhs 120w. and eth 110w. always look what wall says to you.
You are wrong, I'm mining with a rx580 here at 89watts max and I'm getting 30mh per second from the card mining Ethereum, if you are getting 100 watts+ then you are wasting electricity, you need to lower voltage to 850mV