> The speed limit is absolutely not the right single value in heavy rain / fog / snow / etc.

Obviously. The number I suggested is 1) an upper limit not a lower limit 2) a limit, not a suggestion 3) lower than the current upper limit on pretty much all cars.

> The speed limit is also not the single correct value in case of some freak occurrence where it's better for everyone involved to exceed the limit briefly to avoid collision.

Sure. That's why I suggested a number higher than the highest speed limit in North America.