Ok, so it looks like everyone else is getting approximately the same hashrate difference for R9 390 vs. RX 480. I get 260 H/s and 190 H/s respectively with mine (both 8 GB). So my question is, is it expected that the 480 hashrate is only 73% of the 390? Is it because of the lower power consumption on the 480? With every other miner/currency so far, my 480s hash at about the same rate as my 390s. Is this something new with v8.0?
No it is not. It is because 290/ 390(x) are high end cards vs 470 low-mid/ 480 mid level, amd has not released that high performance gpu yet.
470/ 480 owners were lucky to enjoy hig end hashing rates at one algo with some bios modding. Today ancient 290 hashes more than 470/ 480 with the same or better hash/ watt ratio, better get used to it.
ps. what where those every other currencies where 480 matched 390?
While R9 serie has better hash, I don't quite agree about the hash/watt ratio. My RX 470 has better hash ratio than my 290x and the R9 is undervolted, not the the RX.
390*6 1600 h/s 1030/1500 -60mv 1480W(gold psu) from wall (with -100mv 1300W)
480*5 1000 h/s 1288/2100 (mod bios 1750 straps) -60mv 850W(platinum) from wall
actually 390 works at -100mv, but to compare with RX480 I set Vcore to -60mv)
1480/1600 = 0.925 w/h (or 1300/1600=0.8125)
850/1000 = 0.825 w/h
so 390 better)
) watts is hardly accurate either. i can see my 390s being closer to those temps than my 380, no way it's under 40 watts, but there's no way its anywhere near 220 either. 
