I've not read the whole thread, it went a bit awry... however here's my take...

The most accurate guns I have will shoot around 2-3mm c-c 5 shots groups at 20 yards, rested, indoors. With 10 shots, more like 3-4mm.
Take that setup outside, but with no discernable breeze, and i'm more like 7mm at 30 yards. Add in field conditions, resting on a log not a bench, faint breeze, and it's closer to 1/2" (12mm).
Now allow for ranging errors, and an effective KZ diameter on most quarry of around 20mm, it's easy to get 35 yards as a reliable max. Maybe 40 if the range is lasered.

So simple as that really. If I need to get say 10/10 shots in a 20mm KZ outdoors, resting on a tree / log / stump / bipod at a range I'm pretty confident at, it's 35-40 yards max.

Back in the old days when I shot HFT to a farily decent standard, the 45 yarders were always missable, even when you basically knew the range ('cos it was the max), and they had a huge 40mm KZ. And then you had all the time in the world, with a static target.