This weekend we took our 85Kwh Model S from Austin to Plano and back. We maxed out the charge, left Friday night around 7:30PM to avoid all traffic. Arrived in Plano with a 42mile residual tank, and a very slight mileage degradation of about 8 miles - by mileage degradation, I mean that our stated max range was 270 when we left, and if you added up all that we drove + what was left, it totaled 262.
The return was not quite as successful, we lost about 20 miles - and decided to have dinner at the Domain in Austin which also happens to have the Tesla showroom and charging stations. We still cant' exactly pin point the exact cause of mileage degradation - either the heat or wind resistance. Overall, for the life of the car, we average about 350wh/mi; for the trip we ranged between 280 - 322; meaning we were driving a hell of a lot more efficiently than we normally do. We left at 2PM in the afternoon, so the heat was at its max.
Other notable variables - car had 5 passengers, 3 adults and 2 children (and a dog). The trunk was full, frunk rather empty. We operated in range mode both ways, except for the first 45mins of the return trip (can't imagine this caused that drastic of a difference). Best part of the whole trip, is that we charged the battery 3 times on the trip (once when we arrived, once the next night, and for a brief period at the Domain), and we didn't have to pay for any of it. Austin Energy has a great program with Charge Point networks. End to end, transportation to Plano from Austin cost us $10.20 at our current Kwh rate from Austin Energy for the initial outbound charge.
My wife and I took the challenge, and the Tesla passed with flying colors. Have to admit, WACO super charging stations would have been nice, but we were 2 days too early!