Is there a noticeable difference between a silicone implant size of 400cc vs 450cc?
Yes it can make a noticeable difference, not only in appearance but also in the weight of the implant. It mostly depends on your body and the soft tissue cover of your breasts. You can see for yourself as you try the different sizes in your plastic surgeon's office. Best wishes!
There is always a difference in 50ccs in an implant. The difference will be greater in a smaller patient with less breast tissue and less difference in a larger patient with more breast tissue.