re: "Not sure about the slow and medium bit - the words do not enter into my vocabulary"
I always drive at the fastest speed I think I can get away with; however, when you're stuck in traffic there isn't much choice, and I try to avoid speeding tickets, especially out-of-state (several US states are known for speed traps; and in Canada they tow your car if your really push it). On another note, I've been pulled over four times in my BJ8; once by a local cop near Bakersfield, with my young son in the car, due to rubbernecking the view and not paying attention to the speedo, once hot-dogging it on a windy mountain road in Wyoming, once when I failed to decelerate quickly enough in a construction zone in Wyoming--fines are doubled--and once when I passed a California Highway Patrolman who I thought was doing 50 in a 55 zone (turns out my speedometer hadn't been properly calibrated after modification for taller rear-end gears). All four times I got a pass--even though I was so rattled I tried to hand the CHP my American Express card instead of my driver's license--and I got a written warning in Bakersfield. But I don't want to push my luck.
A few times I think I've gotten 25mpg, but I think it's more due to cavitation in the tank causing optimistic pump readouts.
Side note: I thought I'd get a little better mileage when I installed a Lempert 3.54 rear-end gear set, but didn't notice a difference. I think it's because although the engine runs at a slower RPM for any given speed, it has to work harder to overcome the greater load.