I just ordered the 70D after debating these exact points myself.
With the distance between current superchargers, and my driving habits of the past three years (I plotted my routes that I use in various times of the year including winter when range is lowered), I simply couldn't find any situations where the 70's range was "borderline" and the 85's range would be an advantage. Either I'd need a supercharger stop, or I wouldn't. How much juice is left during that stop would be the main difference.
Sure, there might some day be a conceivable situation where I had to slow down or turn down the climate control to make it to the next SC station on a long drive - but not on any routes that I have done recently or anticipate doing. With more and more SC's popping up, the odds of this happening will actually decrease over time, rather than increase.
So, in the end, and for my purposes, the extra money would have been for performance that I don't need (not a track driver, just an everyday "stay on the safe side" driver!) and range that might make me feel better, but wouldn't change where I could or would drive. It's a very individual choice, but I think Tesla came up with a real winner in the 70D - it will cover a lot of people's range needs at a significant price discount vs the 85.