[In Focus]

I'd add hills to the factors to consider. I took the petrol Fiesta on a long run yesterday and was keeping half an eye on the instant econo display - it got up to 10L/100km up hills trying to hold 100-110km (depending on the steepness of the slope). You can compound this if you're using cruise control, because a human being knows to ease off, or even take the foot off the accelerator altogether, downhill. Cruise controls are at their most effective on long, flat runs.