It's only 24% faster
The basic maths thing makes the 1070 19.4% slower than the 1080
If its 30% slower then that will make it slower than the 980ti. Where did you get that 30% number from? It was 19/24% yesterday.
It has 75% of the CUDA cores of 1080, and they're running at 93.7% of the speed. That doesn't even take into account the GDDR5 memory. The compounding effect will be around 70% of the performance. Basic math here:
0.937 x 0.75 = 0.70
That's how I came up with the 70% performance figure, which I think is actually optimistic, given that the memory could be adding an additional performance difference there.
Obviously exact real-world difference in FPS will need to wait until full reviews are out (a couple of benchmark figures usually aren't enough). Until then, I think this is the safest way to look at things.