I have Shimano winter MTB shoes, which are much warmer than regular MTB shoes. When it gets cold, I'll add wool socks, another pair of wool socks, Sugoi Resistor overshoes, and then when even that is not enough (in the teens F), I'll use regular hiking boots on platform pedals. Right now, with temps hovering around freezing, winter shoes, a single pair of wool socks and Sugoi Resistors keep my feet nice and warm.