I've run 95 octane fuel since new.
Around town I get 11L/100, and on the highway I've had it as low as 6.8L/100 and that was fully loaded with 5 of us and the wagon absolutely filled, AND sitting on 140km/h (NT).
38 psi tire pressure.
I run nitrogen also. Some people say its a waste of time, but for me I've driven Darwin - Alice Springs maintained 38 psi, and tires still cool to touch on arrival.
Also I think they extend the life of the tires due to not expanding and contracting.
I get 60***km from a set of 20's
Car has 160***km on it, and only on its 2nd set of tires.