I have a gtx 960 currently that I want to upgrade as far as possible without bottleneck or any other issues...my plan is to upgrade my gpu in a few weeks then upgrade my cpu a year or so down the line
I would feel comfortable with the GTX1070. Your i5 is very strong despite it's low clock speed.
Even the $200 GTX1060 would be a huge upgrade for you though.
On paper the gtx 1070 is obviously much better than the 1060 but in actual practice how much of a diffrence is the frame rates..clarity ect....I'd hate to get the 1060 then a few months later be disappointed because there's something I can't run or whatever it may be...........is it best to stick with nvidia or would amd be a decent option....I've never used amd gpus before and I'm not sure if I should risk going to something unfamiliar....some friends swear by them others curse them lol