I have 5 pairs of Darn tough socks, all Merino.
I have the
1906 - Mountain sock (Bought as my winter sock)
1908 - Full cushion (x2) (Autumn + Spring)
1901 - 1/4 cushion crew (x2) (Summer)
They are the most comfortable socks I've ever had, and they have lasted longer than any pair of socks I've ever had (I destroy normal socks it seems).
The only problem I have had with them is in the middle of summer. On a cycle trip in Luxembourg when temp was 34°C, I ended up in excruciating pain in my feet from the heat. Taking shoes and socks off, allowing feet to cool, then continuing on sans socks solved the problem. Next summer I may try a pair of their coolmax socks to see if they are better in warm temperatures.
I use all of these socks with trail shoes, tho perhaps the 1906 are a bit too thick. The mesh on the shoes mean I'm probably not getting the best out of them that I could. You mention water retention. I've worn the 1908 and 1901 socks in conditions where they got soaked, and yet they were just as warm as when dry (or at least, my feet weren't cold). They dried quite a bit hung under my tarp over night too, not bone dry, but dry enough to avoid much of the cold damp sock experience first thing in the morning.
J