I purchased the R9 390, and Love it, when i got it few weeks ago and I was reading some reviews most said the performance jump vs pricing the 390 is better Performance $ wise.
However if you have the cash for the 390x and that is what you want, then go for it.
I would also considered the 970, but felt that the 390 with more ram might be better future proof as we never know what new fancy gfx will come requiring more ram