There are typically two kinds of roads these speeds are reached in the US:
1. Expressways, where pedestrians and cyclists are not allowed. They are walled off with specific entrances and exits.
2. Country highways, where pedestrians and cyclists are nearly unheard of, and are typically very easy to spot from a distance and adjust accordingly.
There is a third area where these speeds are sometimes reached in urban areas that Strong Towns calls "stroads", and these have a whole host of problems. Going 10mph over the speed limit in these areas probably doesn't make a huge difference, because the are already so pedestrian and cyclist unfriendly to begin with. Not Just Bikes has a great video about them here: https://www.youtube.com/watch?v=ORzNZUeUHAM
It's not uncommon to see people go 20 over on country roads (including mountain roads) in Virginia. That means 55 in a 35, or 60 in a 40. Those roads don't have great visibility, and I've had more than a couple of unnecessarily close calls because of recklessly speeding drivers.
Edit: The upstream thread even has an article where the author describes doing 93 on a 55 backroad in VA and subsequently getting arrested[1].
The comment that this thread branched off of is about the relative difference in danger of 10mph with a modern vehicle, not 20, 30, or 40mph. I don't think I agree with that user's overall point, but I also didn't think your response to it was particularly on point either.
I think our transportation infrastructure needs a massive overhaul to be more pedestrian, bike, and even motor-vehicle friendly, but I think speeds limits are such a poor answer to that problem that arguing about +10mph is merely a distraction.
That was my point. There's A LOT less distance covered by one car than the other, and the speed in that time as well.
An old pickup trick will still be going 35mph at 100ft. I will be completely stopped.
The severity of injury at 80ft for the two is quite different as well.
Of course... I'd never be driving at 60mph if there was a chance of pedestrians. However, the 30-0 difference is even more staggering between older mass market vehicles and modern sportscars.
I take it you've never cycled in Virginia. I have (on "slow" roads no less) and I've had no less than a dozen people buzz me at over 20 miles above the speed limit.
(There is no such thing as a road where people "don't want" to go fast, because "fast" is disjointed in meaning: there's the legal speed that drivers regularly and unsafely exceed, and there's the "fast" speed at which drivers perceive how unsafe they're being.)
To the driving public, specifically. Pedestrians and cyclists will still be goop on your windshield 50 feet into your 100 foot braking.