The worst performing 1070 will still perform better than the best performing 1060. Smaller GPU's cooling typically is not as good as a full size, but the difference in cooling is not as great as the difference between a 1070 and 1060. If the 1070 is priced close to the 1060, then I would go for it.
With that being said, the 1060 6gb is a good card for 1080p/60hz gaming and the 1070 is going to be overkill for 1080p/60hz. So if the 1060 is a good bit cheaper, then it would be the better buy unless you want to move into a high refresh rate monitor (which I highly recommend).