Implant size as a number tells you little about how big and how small they will look on you. It depends on many factors.
600cc seems like a big implant just because of the number "600", but how big they look on someone depends on so many different factors. The most important factors include height and weight, amount of breast tissue, how firm the breast tissue is, characteristics of the skin, and width of your breast base diameter and the shape of your chest wall and rib cage.
With that said, there are certain bits of information that you provided that would steer me against recommending a...