Updated highway mileage results from the last two weeks of wide-ranging temperatures in CT:
1. 12/9/24, 20-25 degrees, 50 miles at 50-70MPH, averaged 3.0 mi/kWh (cabin at 70deg, some heated seat and wheel, some wipers)
2. 12/14/24, ~35 degrees after car sat cold in an open parking structure overnight with 25 degree temps, 50 miles at 50-70MPH, averaged 3.5 mi/kWh (cabin at 70deg, some heated seat and wheel)
3. Today at 52-56 degrees, round trip of 75 miles, heavier highway traffic, probably averaged 55MPH (some 40MPH, some 70MPH), averaged 5.1 mi/kWh (cabin at 70, no wheel or seat heat)
These were reported by the car at destination after resetting the Trip 1 at start of drive. Trips 1&2 had much lower initial efficiency for the first 10 miles, but improved as the car warmed up. I imagine that's battery temperature and the cabin heat working hard. No noticable performance difference in the colder weather.