Realistically, you will see gains around 10% on a dyno -- even with stingy correction -- if we're talking a 20* F drop in temps, all else being equal. Cold temps mean a denser charge of oxygen. Of course it will consume a bit more fuel to maintain target AFR's, but who's complaining?
Also, make sure your oil is at least around 175 - 180* F before flogging it... colder temps also means the oil will be slower to get up to optimal temps.