I'm afraid there's a major difference in the way people view speed limits. 20, 30 and 40 limits are adhered to by all sane drivers, but unfortunately sanity is not tested in the driving test. I frequently see people edging over all of these just trying to get a foot or two ahead of others on the road. After 40, however, it is very much more a question of what are the chances I'll be caught? On motorways in particular 70 is just forgotten about and 80 has become the practical norm. 90 is common in overtaking and I've got very used to the car which appears in my rear view mirror, headlights on and very obviously getting shirty if I can't get out of his way in time so he can proceeed at what must be nearer 100.
On the other hand, I do get a bit paranoid as to whether I'm the one that's dawdling. I was on a long journey the other day and my satnav was telling me that my average speed was 65 when I was doing 70 on cruise control. I'm not sure who to believe now, my speedo or the TomTom.
One final point; I remember as a kid being taken out in a car 'to see the scenery'. Anyone trolling along a country road these days at 40 to give his aged parent or nipper a glimpse of the countryside will be given short shrift by other road users. The 60mph limit on non-dual carriageways is now seen as something of a minimum, not maximum, speed limit.