Here's my story. On Tuesday, in great weather, I left the Centralia supercharger with 220 rated miles. 5 miles from and about 1000 feet in elevation below the Johnson Ridge Observatory, I was at 120 rated miles. My calculation and gut told me I would be fine, esp. since I had already gained 3000 feet. But I chickened out and headed back to the SC. I arrived in Centralia with 68 miles (!) of rated range. So I charged up to 235 rated miles and drove hard back to the Observatory. It was beautiful there. The displays, movie and Rangers are all terrific. For those of us who remember watching that towering cloud of ash and rock on May 18th, 1980, it was quite moving.
I drove hard back to the SC and arrived with 88 miles of range. My Beastie is a standard 85.
This is a great example of how the car keeps surprising me that I get better milage than my (conservative) calculations suggest. I use a 1.2 or a 1.3 factor for google-supplied miles, and I've always beaten that with lots of miles to share. I've yet to experience any of that Brianman excitement of arriving at home with 2 rated miles. As always, YMMV, esp in cooler, wetter weather.