I drive as fast as I judge is safe I know my limits and the limits of my car. On a lot of highways that is well above the posted limit. I leave myself enough space to stop and I stay aware of my surroundings. If traffic is congested or road conditions necessitate it I slow down, often to less than the limit. It's about judgement and I haven't caused an accident in 20 years of driving so I trust mine. Having an arbitrary limit is stupid and causes more congestion than there would be otherwise. Proper lane usage is the solution to traffic problems, not speed limits.