All of the above mirrors my own experience in 39 years of driving.
I have blown past state troopers doing 110 in the wifes Volvo wagon with her and the two setters. I'd see the unmarked car approach from behind and I'd let off the gas. By the time the cop would catch up, I'd be 'going legal'. Every time, I got the stare (white hair and a wife with two dogs does that in a Volvo station wagon) along with the hand motion to 'keep it down'.
Local cops, it has depended on the officer. some are intent on building a career and will ticket people for 1 mph over, others, just want to enforce the law and will not write you up unless you really deserve it (by being a jerk or not stopping immediately).
Unless I am out driving for fun or doing a really long drive (where high speeds can cut hours off of a drive) I rarely exceed the limit. Getting someplace 2 seconds quicker does not outweigh the risk when that is 99% of the driving I do.