1. All roads have speed limit signs, put there by engineers for good reasons. Signs also tell you that there's a school ahead and Traffic lights, a crossing or a turn(which can be dangerous).
2. It takes you 12 minutes to reach a distance of 20 km if you are traveling at 100 km/h. If you travel the same distance at 120 km/h, it will take you 10 minutes. That way, you gain 2 minutes. Although you might end up loosing those 2 minutes anyway when you get caught in a traffic jam or have to stop at a red light.
3. There are special tracks made for racing where exceeding speed limits is allowed where extra precautions should also be taken like wearing helmets.
So: Race on the track... Drive on the road