There's a lot of confusion before a breast augmentation op about the perfect implant size for you.
Silicone implants arrive in fixed sizes, unlike Saline implants, which can be filled with different amounts but generally yield a poorer end result. There is a huge amount of choices. I'm usually shown a picture with the size used for a model that is considered to be perfect. She doesn't consider the rest of her body size and shape when she comes up with this result.
It's important to include lifestyle and sporting activities in your concept. There is no standard for bra cup sizes, which makes it difficult to distinguish between sports bra's and regular bra's. The rule of thumb says that 200cc's is about 1 cup, but this increases with increasing chest as well as cup sizes. A few generalizations have to be made because most requests are for bigger.
I agree that if you are doing it, you should get value. I try to consider the whole person and advise accordingly. We are, after all, individuals, and all cosmetic operations are about confidence and improving lives.