The speed restriction is for below 10,000' inside class b. I know Dallas class b goes 11,000'but at 10,000 you can go fast and begin accelerating above 250. In Houston they can waive this on the way out , they have the procedures and I am sure they will be implemented sometime soon about doing 250 below 10,000' when going into Houston when the traffic is light. The procedure has to be approved by the feds and then it will be published. They also know about the erj being limited to 250 below 8,000' and will say "when able no speed restirction". Also on a fed ride the faa inspecter had said they have been advised that atc was asking for pilots to go 201 to 250 under class b and this is a violation that they are enforcing . Also be aware of when you descend sometimes they will take you below class b and not tell you either. Just be aware and pay attention.