Well this is something that has been available for years. Truckers have it on their vehicles if the company opts to limit the speed that their trucks are allowed to go. The item is called a "Governor". I may have spelled it wrong.
My problem with a governor is this. If you get yourself in to a situation on the highway where you need to have that burst of speed to get out of a situation, it will NOT be there.
Why not trust to the cruise control and commit yourself to using it religiously?