I have Sidi winter boots. I think they are fantastic. I ride into the upper 20sF with no problems. I do not , however ride in rain or snow so I cannot comment on those conditions.

I wear smartwool socks and my feet are toasty. I have not needed booties with them. When it's really cold, I wear silk socks and real wool socks. Mine are a side larger than my summer shoes to accommodate the socks. I bought mine from a fellow TE mate, and they were nearly new.

I would buy them again. I have not tried any other cycling boots, so I cannot make a comparison.