Typically I do 6-8MPH over the limit. If you do exactly the limit sometimes it looks suspicious. Especially when you can hear your car a mile away (well, mine at least) '
Although I was pulled over in NJ for doing 54 in a 50 once

- just got a "warning." best thing to say to LEO when they ask you "do you know what the speed limit is?" is LOWER what you thought it was. That implies honesty, even though its not. If they say "do you know what the speed limit is on that road you passed me on?" (and you KNOW it's 65MPH) say "I believe it's 55MPH, sir" - they are usually so stunned when you say that they let you off. YRMV