The 390 is right on par, beaten just slightly by the 970 in a few benchmarks when at 1080p, but as you move to 1440, and 2k resolution, the 390 starts to get a decent bit ahead of the 970... The downside is, it consumes a good bit more electricity...
IMO, unless you plan on gaming often at 1440p or 2k, stick with the 970 or splurge for the 980. Mature drivers, not as power hungry, similar performance to the 390 at 1080p.
Also, please remember, unless you are looking at an AMD Fiji card, pretty much this whole generation from AMD is really rebranded chips with higher clocks and more memory to use. The only reason the 390 even comes out at higher resolutions is because of it having far more RAM.