Since drag increases with the square of speed, you do get a noticeable efficiency and range hit at 85 v 75. Unfortunately I can’t really quantify it from personal experience because there aren’t too many places around here where you can cruise at 85.
This thread suggests maybe a 25 percent hit?
https://teslamotorsclub.com/tmc/thre...80-mph.266680/
But this is why I’d rent the car and see how it does for you.