I use the Burton Marino wool socks and have used them at -20. Feet were warm. Just curious have you found you needed thicker marino socks? the burton ones are thin...at least as thin as I can find.
On a side note i also gotta give props for the fact they are made in Italy.
burton supreme sock was a thick merino sock, discontinued last year but still kicking around here and there, i bought all i could find, have about 5 pairs
the new burton merino is thinner.
merino is def key