I have a 2000 s6 and its gutsy around town but on the motorway sitting on cruise control at around 77 going to liverpool it averaged between 25-27mpg which isnt to bad for a 4.2 v8.

Its for sale if ur interested

http://www.pistonheads.com/sales/730276.htm

Decent performance without worring about the unrelaible gearbox or suspension (drc) on the rs6.