This thread doesn't make much sense. It all depends on the car. If you have a fantastic intercooler, you're NOT going to see tons of gains from colder weather because your car is already built to resist the heat.

If you have zero cooling mods, then your car is going to run worse in the summer, but gave a bigger gain when it gets cold.

If your car is gaining TONS of power when it gets cold, that more than likely means you have a junk set up, because your car isn't prepared for high temps.