The 1070 is definitely better than the 1060 even at 1080p. The difference I noticed was that the 1070 tended to slow down less when confronted with difficult situations. So it more consistently attained a good framerate.
I am not sure you would notice that much of a difference with the 4790K. Sure on paper it's faster, and benchmarks would be better, but realistically I am not sure you will actually notice anything in-game. If you can upgrade for cheap then sure, go ahead, but I wouldn't spend too much on it. I would concentrate on getting a 1070.