Well, I am playing Star Wars at the highest settings with a Gigabyte G1 Gaming GTX 970 on a Acer XB270HU bprz (2560 x 1440) with 90+/- frames. The cpu is a i7-6700k and the system as a whole scores in the 90-94 percentile on 3dmark tests.
More important to your question is what monitor are you using? If you plan on getting a Gsync or freesync monitor, then let that guide which graphics card you get. The gtx970 and the 390 are about the same price and performance, depending on the model. The g-sync monitor seems to be about $100-200 more than the free sync equivalent.
Lastly, the gtx970 uses less power. Both meet the spec for VR. Neither card will run 4k smoothly on its own. Running two of those cards may be able to run 4k at...