Spa trip 41 mpg! :-)

[ainarssems]

I don't know where you got those figures from.

Maybe we should ask Mythbusters to test it.

It's basic physics - higher speed has higher losses in friction and air and rolling resistance and they increase exponentially with speed. If you drive in top gear the slower you drive the better efficiency is down to the lowest rpm that engine is happy to with which would be around 1200rpm on A8 and 1500rpm on S8. The question is can you get better economy if you drive in lower gear as losses to drive engine and ancillaries remain the same even if air and rolling resistance drops. Please try and report back, I am sure it will be below 50mph and most likely 20-40mph range.