[tertius]

I'm not saying that differential is all that matters. A car doing zero and one doing 20 in an accident is much better than the 80 vs. 70 example.

What I'm saying is apples to apples.

Speed limit is 60, car doing 50 + car doing 80 is a lot more dangerous than two cars doing 60. In both an accident and in actually causing one to begin with.

I agree with most of what you're saying.