I actually tried my hardest yesterday to go as efficient as possible. Did not use brakes at all above 5 mph and ramped up like a snail off every stop. Best I could do is 315Wh/mi, but that is the kind of driving that would piss people off so realistically if I drove like most people, super chill, my average would probably be around 350Wh/mi. So I am not that far off with my current average now between 430-500Wh/mi. So you were right on with the 500 guess as being the upper end.
BTW, how do you calculate you range based on Wh/mi consumption? Formula?