A lot of people will speed and get very little advantage from it. But it costs them gas! The air resistance to your car's motion increases rapidly as speed increases. But the time you save does not. If you increase your speed from 30 to 40 MPH over a ten mile trip you would save 5 minutes. If you increase your speed from 55 to 60 MPH over a ten mile trip you save less than a minute, only 54 seconds. And if you increase your speed from 60 to 65 MPH over that ten miles, you save 46 seconds. That is if you can maintain a steady speed of 60 or 65. What often happens is that a driver tries to go at 65 but has to keep on slowing down and speeding up due to traffic. That acceleration / deceleration goes through gas like crazy.
So think twice about adding those extra 5 or 10 MPH. Over all but very long trips, you will save very little time and the time saved goes up very slowly with speed. On the other hand, you will be paying dearly in gas for that handful of seconds.