Selecting a range of implants should be based on the measurements of your chest wall and what your tissues can handle safely. Selecting an implant that is too big can lead to many problems down the road. It is important that you are seen and examined by a board certified plastic surgeon and have this discussion.
It is rare for someone who is average height and weight to need 750cc implants. Discuss with your plastic surgeon and reconsider or get second opinion if you are ever uncomfortable with the plan.