Let's see:
when I have to travel by car, normally it's to travel more than 20 or 40 miles, most of them on highway. However, it's rare to exceed 90km/h (55mph), and also the 3000rpm.
The car is all stock. The only "mods" I do is removing the radio's antena and over-inflate the tires from the recommended 2,3 to 2,5 bar.
I don use AC, or drive with open windows. I always use low RPM, coast down when its safe to, and slow down by keeping a lower gear. I guess I'm doing all the best practices for a good mileage...
With this, the best mileage I might get is about 4.5L/100km (53mpg?).
The announced milage is:
Urban 7,2 l/100km
Extra-urban 4,6 l/100km
Combined 5,5 l/100km
So, I think the next step should be improving the aerodynamics. Where to start?...