One cannot go by location to determine how much gear you need for certain parts... I have a friend who has circulation issues in his feet and he wears a winter boot with a -90C rating for riding in -30C temps while other folks seem to be able to ride here in normal street shoes with a wool sock.

Key here is to make sure that your winter shoes are a half to full size bigger to allow for a thicker wool sock, don't even bother with cotton as it has no insulating qualities and will make for smelly shoes. If you can't wiggle your toes your shoes are too tight and this applies to any shoe.

I typically wear a medium weight wool hiking sock and will wear that with my clipless touring shoes with covers down to -15C and have sealed the soles with silicone to prevent water from coming in from the bottom. When it gets colder or when I am riding flat or clipped pedals I wear my waterproof insulated hikers and the sock depends on the temperature.

When it gets colder than this I can add a polypro base layer sock under the wool sock and with this I can wear my bikers down below -30C and when it gets butt ugly I double sock and wear the felt pack boots which have a base rating of -40C but have extra felt insoles and these have carried me through -46C / -52F temperatures.

Your socks should come up above your ankle as this is a major point of heat loss like your wrist and head.

I always keep in mind that if I had a mechanical and had to leave my bike I need to be able to walk although walking keeps your feet warmer than riding and getting off the bike and walking a block can increase circulation when the feet get chilled.

The importance of wool and it's properties cannot be understated as it stays warm when it is wet... when I am commuting or travelling farther in the winter I always carry a spare set of socks so I always have a dry pair and a wool sock won't clear out a room when you take them off.

Finally... make sure your head and hands are also warm and toasty to make sure you are not losing heat from one area and feeling it somewhere else.