The 1070 looks faster on paper, in reality its not, the thing with the 1070 is it boosts out of the box between 1800Mhz and 1900Mhz, some even a little higher than that, mine starts at 1911Mhz, but after a few minutes once its warmed up it drops to about 1870Mhz, when its already running at those sorts of speeds out of the box there isn't a lot of room left for overcooking, the average being about 2050Mhz, its 200Mhz above out of box boost clocks, its 10%.
Thats the average real overclock, the 980TI often gets 30% above its reference clocks, so while in reviews the GTX 1070 looks 10 to 15% faster than the 980TI in reality they are about even if not a slight win overall to the 980TI.