I have the HEAVY ROM installed which is supposed to do 31-32MH and does.  However it will crash my system after just running for 1minute every time.  This is for both solo and Dual mining both with risers and direct on the MB.  The power draw at the wall is around 160-220 watts for the RX480 depending on solo or dual mining.  Don't just look at GPU-Z as its not reporting the PCI-E draw from the riser or MB.

The powersaving ROM at 29MH seems more stable.  Using Killawatt at the wall it's pull 185-190.  Deduct 55 watts for my system to get the RX480 card use.  Pretty impressive for 29MH using 130Watts with 16.7.3 driver.  When I upgrade to 16.8.2 I get the same performance but at 15-20 more watts usage.

Will try Boysie ROM next.  

Update - Same stability issues with Boysie's ROM which uses the most amount of wattage.   So far only the Powersaving 29MH ROM is stable for me.