Watch me drive slower than everyone else pressuring them into overtaking me thus increasing the chances of a collision because the government put up a sign that said so.

You're barely even saving any fuel. Maintaining speed uses much less fuel than getting up to speed, and depending on the gearing and aerodynamics of the car it may even be more efficient to cruise above whatever the speed limit happens to be. You're probably costing all the people who have to overtake you a bit of extra fuel, though.

Go the common speed as long as it's within the realm of reason. This is day 1 of driver's ed, people.