1070 is an awesome card, but remember the single pass VR rendering tech is now in the 980ti as well. So a 980ti is good for a couple of years yet. Personally I would go for a 980ti and buy a 1080ti next year. I have a 980ti and I am perfectly happy, I wouldn't be upgrading were it not for the fact I got to do it as part of the step-up program with evga.
Anyway - all this is a bit of guess work, not sure on the prices of the 980ti vs the 1080 nowadays, also not sure how the 1070 compares.