I got a pair of Darn Tough socks a few years ago, and not being able to try them on in the store, I bought in my shoe size based on their packaging. When I got them home, they were far too tight, particularly in the calf. I really don't like anything that is tight around my calf, and the top of the sock was a definite pressure point. Even the foot was uncomfortably tight. I ended up giving them to a kid. I looked at their website and found that they stand by their sizing (I have seen a lot of complaints online about them fitting too tight based on the size), and apparently they do have diabetic "compression socks", but the important thing for circulation is to not have tight points. Anything that comes mid-calf has to be loose enough to accommodate your muscles and circulation. If it leaves a dent in your skin, it is too tight. If I ever buy another pair, I will be more pushy about actually trying them on in the store before spending the money. Based on their durability in your test, it sounds like the materials are generally worth the expenditure, especially with their replacement guarantee. I'll try a size up from their recommendation and look for something with more give at the top next time.
The competitors have more or less retired for the season as I've switched to garden clogs and sandals now that my weather is warmer and I wear both without socks. I'll probably start wearing them again in October.
Location: 7b at 1050 feet, precipitation average 13 inches, irrigated, Okanagan Valley