Thank you for your question. Breast implant selection is an important process and requires good communication between you and your surgeon. Typically, breast measurements are initially obtained to provide an initial guide to implants appropriate for your chest. It's then advised that you try different sizers in a normal bra with a tight t-shirt to get an idea of what your breasts would look like. It's important to focus on the look that you want instead of a specific cup size or implant size. The implants you mentioned are slightly different. The Inspira 415cc implant obviously has less volume and the diameter is 12.5cm and projection is 5.1cm whereas the Inspira 450cc implant has a diameter of 12.75cm and projection of 5.3cm. Both are high profile implants. Be sure to consult with an experienced board certified plastic surgeon. Good luck!