I've been charging to 80%. From what I've seen, if you're driving mostly highway, 55 mph or so, 50 miles is near the limit. 70 is really stretching it, despite what the meter says. I've gotten the low battery alert thrice now. Once on long trip from dealer, twice when I charged to 80% and didn't think I'd be going far that day... Range meter said 70 to 82 miles, and I got low battery at less than 50 actual miles. Could probably have gone 65 miles, certainly not 80.
My advice? If you're going to experiment with charging to less than 100%, be careful. Don't do it with a heavy load, unplanned trips or high speeds. You could wind up in trouble. I thought I'd get two days of commuting on 80% charge (35 miles round trip). Won't work. Need to think like a pilot. Keep a ten to twenty percent reserve.