I've had just over 400miles/tank in the S4 on mostly motorways...before, which I was very impressed with, especially as it has the same size tank as a leon....so works out at 33-34mpg.
Average consumption is ~27mpg, with a range of about 350 miles.
And the "worst" to date was just under 100 miles at the 'ring.
Will see on the 11th if I can do "better" than that at donington