My experience is the exact opposite. I picked up 5mpg on the highway.
It's simple math, you drop the RPMs by almost 30% the fuel economy has to improve.
...
Pure highway trips are indeed bound to show an improvement.
My experience was based on short, daily driven commutes to work, where the engine is just warmed up when I arrive.
Knowing that DickDale also lives in the Netherlands, although in a less crowded area than me, I think he'll only see a significant improvement in mileage if he takes the car out for a 1 or 2 hour trip.
With my 904 + 7-1/4" (3.23 gears) combo I've managed 17mpg once during a day of driving around the country.
These days I have a hard time getting 15mpg on similar trip (3.55 gears), eventhough my engine is better tuned than before.
I will make a 4 hour roundtrip next saturday and will try to get an exact mileage again.
