35 mpg sat at 80 on mway in my 3.0 elite
Instant or average?
Over the course of a tank, I can barely crack 27mpg out of our 3.0
Average! That was with some 120 mph blasts aswell! It was averaging high 30s when I slowed down to 60-70
Either your MID, or speedo is faulty then. 
No it's not, and not it's not. I think your car is faulty, it seems to be missing two cylinders or something hahahahahahahahahahahahahahahahahahahahahahahahahahahahaha
8-)

Are you like 5 years old? :-/ :-?
The 3.0 Estate we have, had from 70k miles, generally get 27mpg average.
Sorry but there is no way on this earth a two ton car with a 3.0 engine, can average 35mpg including a "120 mph" run over the course of 75L of fuel. Either your MID was changed before you owned it, or your speedo is still off.
Driving to south of france on a very, very long run, you may get near that, but not in the UK.
MPG wise, I get 25 mpg easily on gas, but that equates to at least 50mpg. Er so "ha"