I was following my GF in her POS car once, on a LONG road trip. She afraid of breaking down. Her car would shake itself apart at about 85kph.
That trip was the best mileage I've gotten on a tank, about 570km with my V6 Mystique. I set the cruise control around 80kph and held it there for the trip. It was aweful driving like that, but good gas mileage.

I was on fumes when I pulled into the gas station. I think I put like 53L in the tank? Long time ago, don't recall exactly.
On a related subject I drove a Focus wagon last week. I got about 450km on a tank. It pissed me off to have to fill up more often. Grrrr. Must be the small tank, 40L?
Lardy.