I had a nice three hour ride the other day. It was 15 degrees f. I was not cold I just had to come home for something else. On my feet I have at this temp...
fleece socks
chemical toe warmer under toes, in shoe. Only below about 20 f, Shoes not laced too tight.
small sandwich bag over toes.
cycling shoes
larger bag over front of shoe
huge stretched out size 13 socks.
plastic bag, just the front.
neoprene bike shoe cover lined
plastic bag
another neoprene shoe cover
Flat pedals not clipped in no cleats.
this has been working for years. It's as warm as my heavily insulated Sorrel boots, but it's very light and easy to pedal with. I can go for six hours in this temp On the MTB in the snow.