Cold weather Range Anxiety

Well after over 4 months of driving, I was feeling like I understood my Electric MINI E, it's been my regular car for all but 100 mile plus trips. Its been feeling like just a normal car, and I havent had much to report on this blog.
But my sense of normality has been shattered in the last week as Temperatures have plummeted, so has My MINI E's range. At first it seemed like a problem with the heater drawing too much energy, but it has become apparent that even with minimal or no usage of the heater, the MINI E's range has been severely reduced.
This weekend I drove the MINI E to my fiancee's as I've done many times, the ride there showed the first indication of a problem, I had to use the Heater a little bit but not too much it was 41 degrees out, and a bit cool in the cabin, but nothing too bad. I could tell I was using more charge then normal, but I never paniced and though I might not make it. The last 20 miles to her house are on a highway where 80 mph seems to to be the norm, I kept things at 65 mph and arrived at her house 78.2 miles, with 13% charge left and 11 miles to go. Thats a bit low, the first time I drove this I had 27% charge remaining, but it was within my comfort zone (just), as long as I didnt hit a detour, or miss her exit which would mean an extra 24 miles.
so on Monday morning I knew I needed to drive carefully, It was very cold it started at 35 dgrees outside and droped to 31 degrees during the course of my trip, the battery started at 48 degrees but was up to 71 by the end of the trip. At first I was afraid to use the heater, so for the first 20 miles of the trip I was freezing, I would hit the recircylate button every 5 minutes to keep from bringing in the really cold air, I kept the speed to 60 mph on the freeway, and stayed as far right as possible. After I got off the freeway the charge started to climb up and I felt I could afford a little heat before my fingers turned blue (I'd made a mistake and brought two left handed gloves, no rights) For the rest of the trip I'd bring the heater on for a little bit when I couldnt stand the cold, I had the air set to defogger to keep the fron window clear. I realized about half way that when I used recirculate the front window would fog up, but if I let the system bring in outside air it stayed clear, made for a hard choice, freezing or not being able to see. When I passed 50% at the 34 mile mark I knew it would be close.
When I got to 20% and had 20 miles to go I thought I could make it, especially as It seemed to hang at 20% a long time, but the last 10 miles to my house are on the freeway and up a very steep hill, I had to bring the car upto 60mph and was still passed by double trailer semi's going up hill. I reached the top of the hill with 3% charge left, after that it was all down hill and back roads about anouther mile to my house. I arrived with 13% charge and 11 miles to go.
I've driven the MINI E 5000 miles in 4 months but this may have been the last time I drive the MINI E to my Fiancee's house until Spring as it was just too close, and too cold. I was thinking if there had been freezing rain and I'd had to keep the defogger running at max heat to keep my window from freezing I wouldnt have even got half way, add to that the fear of being traped in the snow without heat and I dont think I'll be putting as many miles on #304 going forward.