That's the point i'm downgrading 
The a6 2.6 v6 is only 150bhp, its a lump for torque not power.
Compared to running the A8 4.2 V8, its going to be cheap on fuel 
I expect it will be sh!t, but you never know!! then i will have to make a decision 
:lol: I had a A8 Quattro 4.2 V8 for about 6 weeks last year. I was kidding myself when I bought it that the mpg wouldn't be too bad, even taking it uber gentle it still only did 20mpg. Otherwise it was a great car, swapped it for a A4 Tdi though.
OK non VAG but Saab 9-5 Aero's are hard to beat, mpg in the 30's and faster than the A8. Just looking for one myself at the moment.