erig007

Agree neoprene socks are like my neoprene diving boots it worked for me with just those boots with socks around freezing temps and below that it required wool felt liners inside + some others tricks (VB socks, toe warmers, shoe covers, toe guard etc)
i reached -36C/-33F without the 40mph windchill for a 5hrs ride last winter here in Canada with these but it required lots of work.
My main cons is that there isn't usually much room on the toes area and because it is stretchable it was a pain in *** to put on.
My main pro is that it is comfy and quite cheap (but price can add up pretty fast with all the add-ons).

Agree with the necessary room for layering purpose. It is key for warm feet. Until recently i though that it was possible to make nearly any boots way warmer by going 2, 3 or more size bigger for layering. If i believe it is possible to easily make some 30F rated cycling shoes able to handle 0F I believe it is way harder to make the same cycling shoes able to handle -40F due to the design.
I did succeed with my diving boots though but it wasn't easy. The size and shape of diving boots is pretty similar to the cycling shoes one

There is a limit to what you can easily do and it is related to the height (especially at the toes area) and the width and the outsole thickness of the cycling shoes most of the time. Chances are that your layering ability will stop with your toes or feet being too tight with the additional layers in those cycling shoes even if you can find a bigger size of these (except if you want clowns shoes). Why because the cycling shoe is not high or wide enough. The Steger Mukluks (arctic, yukon and camuks) and some other mukluks brands as well as some polar boots are usually wider and higher especially at the toes area than most cycling shoes so going for a bigger size allows more room for the feet in all directions height, length and width limiting the problem of tight toes and tight feet (width).
Going for Neos overshoes is an easy and viable solution to increase warmth of cycling shoes though but it also means another layer to handle which means a little bit more hassle, some trade off in terms of esthetics, some additional cost, a little bit less stability and no more SPD. Cons which could matter for some and not for others. By the way cycling shoes covers are useless against losing heat through the outsoles.
Furthermore, regarding the layering of socks with my big feet i can't find any socks big enough to be the third layer, the second layer of socks being already pretty tight so i use felt liners instead of additional socks.