Getting implants often yields an increase in income, but it's hard to say how much is from the boobs and how much is from the increased confidence that came from getting the boobs you want.
However, it wouldn't be accurate to say that a certain type or size of boobs makes more than others. People aren't just tipping boobs, they're tipping a model who has a personality and a show style in addition to her body type.
Hell, even if we're looking at strictly income and boobs, let's use the MFC top 20 as an example - there have been many different girls with different sizes and shapes of boobs ranking up in the top spots, including small or less perky ones. It's not all big round tiddies, in fact I usually see more girls on the medium-small side up in the ranks.