Hi Redscotti,
The point of the arrangement of plastic bags and socks I suggested was to keep the socks between the 2 plastic bags completely dry and of optimum insulation. These dry socks keep your feet warm. My (unavailable to you amphibian socks) keep my feet dryer than a single plastic bag would but my feet are still a little damp. They can still get cold. The 2 plastic bag idea works best when it is very cold, below freezing. At minus 10 C I ended up wearing my thin Merino socks then a plastic bag then thick socks under my Goretex socks just for warmth. Then It occurred to me once I was wearing a plastic bag to keep the thick socks dry from my sweat the goretex socks were not needed. I did not need breathability just waterproofness. Another plastic bag would do just as well.
Once you are working on the vapour barrier principle you should control your body temperature so your feet are not hot enough to continue to sweat. In the sort of cold temperatures I am talking about you dont want sweat anywhere. It chills you when you stop.
I am actually experimenting with a vapour barrier suit but it is not often cold enough in the UK to really trial it. The one good test camping on the Cairngorm plateau last winter it showed potential. Same idea: thin merino layer then homemade silnylon all over suit then down insulation, kept dry from my sweat by the suit then a waterproof layer which is only breathable for the times when not wearing the vapour barrier suit. The merino layer gets damp but everything else is dry. I think I needed noticeably less layers than I would have otherwise. The suit is designed to come off in pieces without removing the top layers.
KISS principle:
if you can cope with wet feet do.
If your feet are too cold, experiment with my suggestion of plastic bags. They don't cost much if it does not suit you.
If not then Goretex socks are available. at least the Gore bikewear GT. Unfortunately I think walkers wear them out quicker than cyclists. I wore a hole in the heel very quickly. Replacing worn gore socks is a little cheaper than replacing leaking gore boots! Some people have better luck with sealskins than I did, if you try them, be gentle washing them. I am sure you can tear the membrane just by stretching the knit too much.
Edited: 27/02/2012 at 11:10