I ride a 50 pound extracycle in the winter...

It runs smoothly at any temps (synthetic grease ftw) it's weight does affect my top speed a little but I am still faster than most winter cyclists because of the incredible stability of the bike.

The biggest impediment to speed in the winter tends to be wind resistance as the air is denser and we are less aerodynamic... that and riding your bike at 40 when it's -40 requires snowmobile gear to stay warm.

Many athletes perform at high levels in the winter... biathlon and cross country skiing come to mind.