A couple of the western counties have 90km - I think Bruce does as well on their county roads.
I agree that inadequate driver training is a problem.
Speed differential is a concern. Some of the 401 stretches with heavy truck traffic but are still 4-lane would be a concern. I would also like to see legislated minimums as well so long as there are alternate routes. Some US jurisdictions have a maximum, a truck maximum as well as a minimum. I don't know about Europe.
I would be interested to see variable speed limits tried in problem areas. There is a stretch of Quebec 20 that is susceptible to fog that has it. Doing it on a wide scale would likely be very costly in terms of signage, networks, control and management, etc. Areas of Simcoe County experience lake-effect snow streamers that come and go in a blink that would be difficult to manage. I also don't know how the enforcement aspect works in the other jurisdictions.