Aye, overly thick socks aren't good because your feet will get squashed and that'll restrict the circulation. Merino-based thermal socks seem to strike a good balance between warmth and thinness in my experience. Insulating overshoes also do a good job but I prefer toe covers because you can just leave them on your shoes rather than fannying about taking overshoes on and off (which as
BabyMurloc says, is a right pain in the arse).
All that said, I've still found that my feet tend to get cold (and numb toes are just horrid - I've actually fallen over after getting off my bike because my feet had gone numb. Not nice.) After putting up with this for a few winters, this year I've taken a different tack and bought myself a pair of proper winter boots - in my case,
Shimano MW701s (aka MW7s). I snapped them up in the pre-Black Friday sales for £120 and although that is quite a lot of cash for a pair of shoes, they have been absolutely bloody brilliant so far. Almost totally waterproof (weak spot is water running down your legs into the ankle cuff, but can be mitigated by fashionably wearing your bib tights over the ankle closure rather than under it, or fitting a tape "gasket" for longer rides) and very, very warm - I've been out in -5°C weather and my feet have remained warm, even though my fingertips (wearing thick outer gloves and merino glove liners) have been frozen. They're SPD-cleat only, but I'm a commuter not a racer :) No more fannying about with overshoes or toe covers, no more cold toes, no more wet feet or trying to dry off socks, shoes or overshoes at work. Also means that my non-winter shoes will last a lot longer as they're no longer getting soaked on the reg (and they won't stink
quite so much either!)
Slight criticisms would be that they're not light (about 450g each, although that's actually only slightly heavier than my normal shoes + thermal overshoes), the BOA dial is a pull-to-release effort rather than a two-way dial, and they are slightly more true-to-size than my other Shimano shoes - probably because they anticipate you wearing thicker socks, as discussed above. They could possibly do with a second BOA dial too, but that would probably compromise the waterproofing. Oh, and if you do get them properly saturated, they take an
age to dry out.
I also tried on some Northwaves (GTXs?) which seemed great, apart from one minor issue... I couldn't get my feet into them, as the ankle opening was so narrow. I'm sure that once on they would be grand, as the seal around the ankle would be nice and tight, but even trying on the biggest size they had in the shop (far too big for my feet), I just couldn't get them on.
