Sorry Simon, disagree with you 100%
Ok, of course I can judge speed and distances, I'm pointing out a simple fact that pulling in and out over what may be a 4 hour-8 hour journey - or any journey - would definitely lead to more chance of driver error.
I don't know what motorways you drive on Simon, but on the M1, M62 and A1, you get very few people doing 70mph dead on. We are talking realism here.
For many years, the AA and other credible motoring organisations have said the speed limit is too low - look at Germany - where there is or was no speed limit on the Autobahn's.
I would say at least 70% of motorists go faster than 70mph.
Regarding you third point; of course that's true, but again in the real world, many drivers do not leave enough of a gap - I do.