You are using an out of date browser. It may not display this or other websites correctly. You should upgrade or use an alternative browser.
I have been calculating metrics on electric car efficiency on my blog. Ton - Miles / kwH seems like a good metric to judge the engineering efficiency of the car. It isn't as practical as a day to day MPGe or Miles / kwH, which I prefer. But it does provide an insight into the engineering built into the car.