I normally go to the speed limit. Very often I find myself being tailgated by a truck -and it is almost always a luxury truck or SUV- and when I move out of the way, they accelerate to 80 or over 90 mph. (The upper limit in the city is 50) Really, some people have a cause, some just want to see the world burn, and some just don't give a damn...
Anybody driving slower than you is an idiot, and anyone going faster than you is a maniac.