With high power cost maybe the 1070 ti would be a really good option for you. Being able to cut the power down to the cards to save on the power bill. 1060's also do really well undervolted. The cards run cooler which should help with longevity. I'm a big fan of the 1070 ti myself.
I see your thought process here and I'm thinking the same way what's the best computational per to Watts. But I also want the cards to be able to ROI in the estimated 190 days. I feel the 1070 and 1080 both to and normal edition will continue to mine effectively with increases and difficulty as they are newer cards. I'd be worried about the 1060s hitting ROI or still profitable after this time.
So I guess is the question is what's the better hash to watts. The 1070 or the 2070ti. Price difference is that big right now between the two cards. But I am seeing the 1070 when clocked accordingly can perform the 1070ti, but at what wattage cost is the question.
I still have some research to do! =]