Put this in another comment, but social conventions for driving vary a lot by region... in the US at least. Can't speak for anywhere else. In Chicago, if you're driving the speed limit on an interstate, people just assume you're geriatric or stoned. The flow of traffic is consistently 10-15 over on all Chicago area interstates. Cops do 20 over. But, in the Bay, unimpeded flow tends to rest at 0-5 over.

As someone who isn't a speed demon, I still like the police warnings because it's a timely reminder to check myself. Am I matching the flow of traffic? Do I blend in? Am I making myself a target?