@Tom GR - Ok but vram can occasionally be an issue at 4GB but it's not too much d a problem. I would be concerned with SLI 980s at 4k though going forward.
@titanpilot - 390x is a great card for sure. But if I could be willing to stump up the extra cash, I would definitely go for a 980 as its a better card by way more than 4% when overclocked. If you don't overclock it, the 390x is on a par "trades blows", it really comes down to which games you play when making a selection. I don't think you can say 4% as that is just a statistic from one sample of games. A different sample will show different results, some which will favour the 390x as the margin is so small. I'm backing the 390x to possibly be the better card at stock speed going forward (directx 12)