The 1070 is the intelligent buy right now, the 1080 is pretty much irrelevant now for anything but Willy waving, it's not quite capable for 4k but the 1070 is good enough for 1440p.
Also for a little more than the cost of a 1080 you can probably buy 2 x 1070 and get a lot more performance, coupled with the dx12 mgpu support when it comes it is a kinda no brainier for me.
This is Nvidia putting down their marker again and AMD have to come out strong now to stand any chance of competing, slot hinges on Nvidia pricing of the 1070, and the unknown quantity that is Polaris.
As it stands now the 1070 is the card to buy until true high end arrives, AMD need something special or its another 970 sales spree coming with the volumes these will sell in