Iain, I agree fully with you. My U2150 has fast axles and Claas overdrive, but there is no way for me to keep up with the cars. I have never intended that that when going for fast axles and overdrive. I use the overdrive to keep the rev down.
For example when driving on the highways in Europe, most commercial trucks are limited to 90 km/h and I use the fast axles and the overdrive to be able to cruise comfortable with the speed of the trucks. I can go faster and overtake the majority of the trucks ... but at the same time it is not safe to overtake every truck that is going 90 km/h as highways can be quite busy and truck can form long columns, so I prefer to more or less keep at about the speed of commercial trucks and overtake only when necessary. There is no point in competing with cars ... it's neither possible nor safe either.
For example when driving on the highways in Europe, most commercial trucks are limited to 90 km/h and I use the fast axles and the overdrive to be able to cruise comfortable with the speed of the trucks. I can go faster and overtake the majority of the trucks ... but at the same time it is not safe to overtake every truck that is going 90 km/h as highways can be quite busy and truck can form long columns, so I prefer to more or less keep at about the speed of commercial trucks and overtake only when necessary. There is no point in competing with cars ... it's neither possible nor safe either.