I think the 1700 would be better.
A friend of mine has just bought a GTX1080 ti and he has a i7 6700k.
He plays at 4k with everything max and with wow, he has fps dips as low as 20fps.
With his former maxwell based card, he never had this issue with the i7 6700k @1080p but did had a similar issue with his former older generation cpu (core quad) @ 1080p.
No way that the gtx 1080 ti is responsible for that, it is highly likely , that the mighty i7 6700k cannot crunch and push enough data to keep the game above at least 60fps at 4k with max settings. This is a DX11 game, so highly likely, the cpu cannot push enough drawcalls out.
That is something to consider for anybody who wants to play at 4k with max settings, that demanding games will max out the cpu with the current gpu beasts availabe. It is not for a reason AMD is pushing 8 cores. Vega needs a cpu that can keep it busy. Even with DX12 and vulcan this issue will still be present. Especially large fields with lots of players as is often the case with online multiplayer games.
And of course, for Nvidia designed gpu cards the same principle applies.