"Over 9, pay the fine". I can't speak for all jurisdictions, but when I was a young man working in a car wash, we washed the police cars of a few nearby communities. It was routine for them to set their radar for 10 over the limit or more. Based on my driving experience, that is still generally true, though there are likely exceptions.
That is my “rough” rule as well on an interstate. When I drive the “super” two lane highways with a 65 MPH limit, I keep my speed at 69.... tops...... It seems that you run into the county sheriffs who are interested in filling their respective county’s coffers.
My opinion.
MFO