Another thing today is most cars have 2 speedometers, both digital and analog. And they're a lot more accurate than they were 40 years ago. So there is no reason to be caught going over by any number.
The problem is most of the people on the road all feel there is a 8 to 10 MPH or so, "safe buffer", that most cops will allow you to exceed before stopping you. Because most of the time there is. So it's going to take a lot of tickets for going 4 or 5 over to, "get the word out", in order to stop that kind of thought.
And many times I've been on the highway cruising along with a pack of cars, all going 8 to 12 over the limit, sometimes more. They all feel there is, "safety in numbers", and the cops won't pull anyone over.
And with auto insurance costs astronomically rising today, being found guilty of ANY kind of moving violation could spike your insurance rates to the point of non affordability. Especially for a lot of young people.