My 2x RX 480s came in today. Some preliminary testing and brief conclusion.
Stock voltage definitely too high for stock clocks.
It had 1150mV @ stock clocks. At everything auto, it was boosting to around 1190mhz during benchmarks.
Not even 1266mhz boost clocks.
I manage to get it stable at 1100mV, but actually OC to 1.3ghz.
It was stable at this clockspeed at +5% power target. At default power target, it was hovering around 1288mhz.
Both card behave similarly, the 2nd one would tolerate lower at 1085mV @ 1.3ghz, but I saw artifacts in the benches, so I bumped it up to 1100mV.
My conclusion is AMD's power management is fail because it's defaulting to too high voltages for stock clocks, at each power state.
Other things I've noticed, fanspeed on auto is worst than on manual. It heatsoaks due to slow ramping, and it gets to around 83C with 2200 RPM and stays there. On manual setting, I just set the temp target max 80 and target 80, and it ramps up a lot quicker, reaching around 1800 RPM to get ~78C. Basically, it's quieter & cooler with your own temp target of 80C.
And this card is absolutely not noisy at all. It was barely noticable above my other case fans even at 2200 RPM.