My wife and I each have 3's and our mileage is very close.
On my 04 Sport 5 spd I averaged 7.5 L/100kms mixed driving. Her 08.5 GT auto gets about the same on the pump with her computer reading slightly higher than what I record at about 8.7.
I haven't had the Speed 3 long enough to tell anything yet, only at 700 kms. The computer is telling me 8.6. We will see....

