You don't have to guess. The linked article has two graphs showing the range obtained at speeds ranging from 40 mph to 85 mph for different models. For the 85

You don't have to guess. The linked article has two graphs showing the range obtained at speeds ranging from 40 mph to 85 mph for different models. For the 85 KWh battery pack going at 55 mph you'll get about 350 miles of range. Going at 85 mph you'll just over 200 miles of range. That's slightly more than a 40% reduction.