Earlier quoted context omitted.
I think that's stupid for one reason. As an engineer I often considered 10% tolerance to be sufficient. I think enforcing speed limits to anything greater than 10% is just silly. I often drift +/- more than 10% of my intended speed. It's just human nature. I pay more attention to potential dangers and obstacles, and less on whether I am within a % of the speed limit, and I really hope other drivers do as well.
Speed limiters and cruise control are pretty common in modern cars. You can set your mental intended speed lower and won't drift as much. This is from experience of switching to a car with speed notification beeper (very low tech) - it took maybe 2 weeks to stop drifting over almost completely without paying extra attention. We ended up treating it as a game with gf - shortest time for a 300km drive with no beeps.
Never heard of a speed limiter. As you can probably tell from the "freedom units," I'm from the US if that matters.