Yeah that's often the case with new versions of DirectX, some extra effects that are subtle and kind of nice but not usually a huge impact and worth the performance hit.
I know the older cards can do 12, see the image I posted comparing the performance!
They also said for VR they don't strongly recommend the 1080 over the 980Ti, it's a little nicer with current games in some cases but not much. Devs would need to start coding for the unique VR specific features in the new series for it to shine, but that hasn't happened yet.
Full article here
http://www.roadtovr.com/nvidia-gtx-1080-benchmark-review-performance-head-to-head-against-the-980ti/