I’m a regular traveller on the A9 from Pitlochry to Dundee, Perth, etc and back, I find that the speed limit thing is when cruise control comes into its own (plenty of folk go screaming past me though, perhaps they don’t know,the definition of average?). The main annoyance on the A9 for me, is the 50mph limit for 7.5 tonnes and above, it’s not the vehicles that should be observing this limit, it’s the cars that think it applies to them too.