Had a go on a 1070 yesterday on Witcher 3. Monitor - 1440p widescreen (3440). Tbh, I weren't overly impressed. Seemed marginally more smooth than my 980GTX but not the killer card everyone is making it out to be. Weren't overclocked as it's going into a prebuilt system for someone and we didn't what to risk it. Might be a bit better overclocked but I feel at this price point ... I gotta be crazy to get it at this price.
Viewing the performance firsthand makes it easier to forget about this whole business and wait for the Ti or Vega.
However, for a more 'normal' 2560x1440 it might play better.
For 1080p this thing will be a monster.
The 1070 is a 980Ti, there's nothing "to be impressed" or new about it.