I can say for sure that for me my 5.0 supercharged Jag is better on fuel than my 370z was , I would average 22-24mpg out of Reggie the Supercharged one and 24-26mpg out of the n/a one , 330-350 miles before the light comes on, its a big tank on the zed
The Jag is doing 25mpg on average.
Dont trust the on board display and certainly dont trust the range estimator , mine went from 45mile range to 0 in less than 20 miles