Take a peek at Flight Aware for almost any Class B at which you look. Right now, KORD, 4000 msl 280 kts for a SW 737. Night, junky weather, 1am local, so not much glider worries. But, it has been my observation there are not many air Traffic Cops worried about Part 121 speeders. Perhaps that is an entirely different thread.

Cindy B, excellent points made in your post.
Regarding the speeds, I have found ATC very diligent at monitoring speeds. I've been asked to verify my speed of 250 Kias or less, several times when I am right at the limit. ATC does not even have authority to approve more than 250 Kias. They can approve an increase above the 200 kias limit under class B or in the vfr corridor of class B, but the 250 kias limit is a hard limit. Looking at the flightaware speeds is a little misleading because those are true speeds, does not factor in winds, and are computed based on position change. There is no way to know exactly what the indicated air speed is for the aircraft at a specific point, unless you are in the aircraft.