Personally I would stretch for the GTX 1080 on June 10th. With the GTX 1080, you'll be able to do 1080p @ 144 Hz with either MSAA or Nvidia SDR. A $400 max budget plus you could gather at least $125 from selling your used EVGA GTX 960 (http://www.ebay.com/sch/i.html?_from=R40&_sacat=0&LH_ItemCondition=3000&_nkw=evga%20gtx%20960&LH_Complete=1&LH_Sold=1&rt=nc&_trksid=p2045573.m1684). My guess is that the GTX 1080 (non-founders) will sell for a street price of $550. If that's more money than you're comfortable with then yes, purchase the 1070.
*** quote about Nvidia pricing of GTX 1080 and 1070 ***
"The GTX 1080 drops on May 27th with the GTX 1070 to follow on June 10th. The 1080 is priced at $599 while the 1070 will cost $379...