Do NOT get the GTX980Ti.
Raw performance in current titles is only one aspect. The GTX1070 also offers:
1) DX12 asynchronous support (dynamic load balancing, preemption etc)
*This isn't just for increasing FPS, it can help make the game smoother. Many games stutter due to a lack of this feature.
2) VR support:
Up to 1.6X higher FPS using a single-pass render approach for both images. Meaning if the GTX1070 and GTX980Ti were both tied at 60FPS normally, the GTX1070 would get 106FPS now in this case.
This is pretty critical for VR since GTX980Ti isn't too far above the GTX970 minimum VR Ready capability.
3) Much less heat output->
It's not just the power, those extra Watts can make a big difference to room temperature.
4) HEVC, HDR, higher DP/HDMI bandwidth (mainly for future monitor and encoding techniques. HDR means High Dynamic Range for much better color reproduction on coming monitors).
Higher bandwidth allows high resolution, high bandwidth and HDR (all add to the bandwidth requirement).
5) Ansel:
2D and 3D snapshots. Cool feature.
6) Triple-monitor, audio feature (sound bounces off objects), VR don't apply to current titles (though some may get plugins... such as Fallout 4 which is getting VR support).
7) 8GB vs 6GB
Summary:
Most of the is for the future, but some of the features like DX12 are very, very important for the long-term.
I advise you to do more research.
Yes, I would WAIT and get a good non-reference card like the MSI version or similar with great cooling to minimize thermal throttling.