Depends how fast everyone else is going. If I'm the only one on the road, then I'm going the speed limit. Don't want any cops using me to fill their quotas. If someone zooms by at 15 over the limit, I call them a canary, checking the coal mine for speed traps. If they don't get pulled over going 75 in a 60, then I can safely go 65.

If there's a bunch of cars all speeding, then I'll keep pace with them unless they're going over 70. At that point it just isn't worth it to exponentially increase the energy of a collision while logarithmically reducing the time it takes to get to my destination. I'm not going to double my kinetic energy so I can save 15 seconds on my trip.

...wait, I think I misunderstood the question