Thing is... who is going to buy this card exactly? I will because it will be an upgrade from the 380 4gb I have, but anyone with a 390 is likely to only get a side grade.
i have a 390 and im going to pick one, mostly because i am tired of 28nm and want the finfet, also want it for the extra features, and another 15-20% performance at stock isn't that bad especialy if i can overclock it further to Fury.
and because i think it will hold value much longer, so even if i want to sell it later on to get on vega, it would hardly lose 50€, beside the price/tdp/size/heat, makes it easy to crossfire later if i decide to.