Yea that's about right. On google maps rt now (with traffic on my end) it spits out 500 miles even, 7hrs 25min. Limit is 70, I go about 75, make up some time there. Stop for 15 in the middle. Typically arrive in 7 and a half hours. My EPA MPG is 17/23.
So if you get a new model S with a 373 mile range, you will only have to stop once after @ 300 miles to eat. You will have @73 miles left and if you have a more "relaxed" meal - say 30 minutes instead of 15 - you will probably have added at least 200 miles to your range - more than enough to get to your destination. Your fuel costs will be zero and you will arrive far more relaxed because the car will have basically driven you the whole way.