Guys who like big boobs probably wouldn't like them if each one is several times bigger than his head. So bigger is better up to a point.
Girls who are size queens don't want an 18 inch penis. Even 12 inches is probably too long. Most say that 9-10 inches is the longest they can go.
Girls who like to date guys taller than them have a limit. They probably don't want to date a 9 foot tall person (the world record for tallest person).