In my experience a 1070 isn't always 2x, better 1.85 if you compare it to a 970.
It depends a lot by the algos. I've got a very complex chart and these are the ratios.. (personal use, I can't share it right now)
It's not about what is already written, rather new optimizations that are made for Pascal specifically. The 1070 has been out for a little over a month. Those algos weren't written with Pascal in mind. Lyra with the improvements written by Nanashi were made specifically for the 1070 and it shows.
If it can be double for Lyra, it can be double for other algos... save Dagger as that's a very special case scenario. There are very few algos that peg the memory controller.