Speed limits are posted for the safety of everyone on the road. The speed indicated on the sign isn't a suggestion, its an order. The people who set the speed limits don't pick random numbers and change it from one section of a road to another just to play a game with the drivers using those roads. They use carefully gathered information about such things as the road surface, degree of turns, and grade of hills. They can then use computer modeling to determine how long it will take a vehicle to stop at various speeds or the forces caused at various speeds which would produce roll-overs for different sizes of vehicles. The results produced are the safe speeds for the use of that section of the road by every type of vehicle utilizing that road.
      Other speed limits are set using the same information while adding in factors such as driveways which can't be seen until you're within a set distance, the number of side streets joining the main road, and the number of pedestrians using crosswalks. School zones have even lower limits because some kids have the tendency to run across roadways without looking for cars. The maximum speeds are set, not only for your protection, but also for the protection of everyone else using those roads.
      Specialized driving skills don't give you the permission to drive above the posted speed limit. Unless the state in which you're driving makes exceptions for emergency response vehicles, including private vehicles with the appropriate lights, you're bound by the posted speed limits. When driving a privately owned vehicle on private or personal business and errands, your specialized driving skills mean nothing. I've held many jobs in my lifetime and have been certified to operate ambulances. I never lost those driving skills when I was working for the service and went from an ambulance to my car in order to drive home. Some of those skills come in handy such as when an animal runs out in front of my car or someone else swerves into my lane of traffic. The point isn't that I can do those things, the point is I have no legal standing if I purposely put myself into those situations because I'm driving over the posted speed limit.
      Probably the worst excuse for speeding is "I'm only going that fast because everyone else is". This is false logic because everyone is thinking the same thing. If you slow down so you're obeying the law, the person behind you has to slow down. Ignore the fact they're flashing their headlights at you or give you obscene hand gestures as they speed past you. The more people who do the posted speed limit, the more people will slow down because then they'll be doing the same speed as everyone else.
      Or you can go ahead and use faulty logic as excuses. If you do, don't complain when you get pulled over and issued a speeding ticket.