I have 2 "full time" ETH mining rigs, one a triple R9 290, one a dual R9 290.
I have other rigs that bounce around, mostly between ETH and ZEC, depending on profitability.
I mine through pools.
So i could be profitable with a 390?
If your electric cost is low enough.
The "triple" rig is pulling in a little over $3 a day right now. At the electric rates for residential or small business use (not the same rate, but VERY close) where I'm at, it goes through about $1 of electric a day.
"double" rig is $2+ and about 65 cents respectively.