I'm with BanditDave. My aim is to get there safely and ideally, have a relatively relaxed journey. A few minutes this way or that, and that is the most you can save, even on a long journey, doesn't matter. The only practical way to continue using the motorway system is to have some degree of control to both optimise use and optimise safety. Anything that can be done to prevent accidents, apart form its ethical value also has a practical value in that we reduce delays, frustration and improve efficient usage.
Last week, I was in a hired van in Germany. My pal had a Tomtom which bleeped whenever I went over the speed limit, which I did inadvertently twice in 500 kms. The effect was to remind me and subsequently I stayed below the limit.