Should I wear two pairs of socks for extra warmth in extreme cold?

Absolutely not. Wearing two pairs of socks is one of the most common mistakes in skiing. The double layer creates wrinkles and folds that cause pressure points and blisters, restricts circulation by making the boot too tight, and traps moisture between the layers. One quality heavy cushion merino sock provides better warmth than two pairs of any socks. If your heavy cushion sock isn't warm enough, the solution is better boot insulation or heated insoles, not a second sock layer.