475 cc HP is a reasonable size for you. However, implant size and cup size do not equate well, and cup size is an inexact measurement as it will vary greatly among bra companies and even within the same company.
The size of the implants is based on a combination of a patient's goals and objectives and her anatomy. In order to provide a natural looking augmentation, the surgeon needs to evaluate many factors including soft
tissue coverage, skin laxity, chest wall width, breast imprint width, the shape of the breasts and relative level of constriction to ensure that the breast implants are appropriate for your body.
Breast Augmentation Options
Your question is a good one and brings up an important point, that different surgeons may have different suggestions for patients, and that more than one option can achieve a very nice result. Your surgeon's plan seems reasonable but without an examination it is really difficult to know. Other options could include different sized implants or staging of the procedure. We can never guarantee a cup size and this is something I stress to my patients-- what matters more I think is that the overall look, size and shape meet your goals. I would have a good discussion with your surgeon about your goals and concerns prior to surgery to make sure the two of you are on the same page.