I can't find a single article saying anything else. The 20-25 degree maximum temperature drop seems to be everywhere which leads me to think it must be true but

I can't find a single article saying anything else. The 20-25 degree maximum temperature drop seems to be everywhere which leads me to think it must be true but I don't understand why. I'm trying to find out what happens if you go oversized on a variable speed system and can't find any information.