The socks arrived so, after a wash, thought I'd try them out today - in normal circumstances for now, to gain a fair comparison; dry feet in my usual boots. I had two pairs of socks to try, the main ones being the darn tough tactical full cushion sock and also a pair of smartwool hike liner socks.
Unfortunately within just six miles, the tops of some of my toes were being rubbed raw, which was unexpected. So I swapped the main sock to the inside and put the liner on the outside (unconventional obviously, but it maintained the same total thickness for testing purposes). After that things were considerably better, and a further 11miles caused no more damage to the tops of the toes, though I did develop a blister underneath one.
This is just a local ~17mile route that I've been doing around twice a week for the last year, and 'never' had any foot problems resulting from it whatsoever. So for my feet the merino liners worked far less well than my usual socks, and surprisingly also less well than the thicker merino socks (presumably due to the nice loop-pile against the foot), which rather defeats the purpose of using a liner.
The main socks were pretty comfortable and cosy, so I'm much happier with those. Though based on this I might want to team them with my usual synthetic (tactel) liners, which have never led to blisters. I'm not sure if that would make costly merino somewhat wasted, or if it might be a match made in heaven. Probably it depends on how well they deal with warm wetness in the summer.