You certainly get increased performance with cold weather, due to the nice dense air the engine is inhaling. Just make sure the motor is at operating temp and enjoy
To calculate the power increase, you must look at the temperature to air density (which is also affected by humidity and barometric pressure) relationship. Standard atmosphere is sea level and 15 degrees Celcius with 29.92 inches of mercury. Its a bit late to be doing the math right now, but perhaps someone in a less intoxicated state can elaborate further from here
Goodnight gentlemen
Patrick