Concerned about size. Would a 450cc implant look large and unnatural? (Photo)

 Thank you for the question. 
 Based on your photographs, I think that you are starting at a good place and should have a very nice outcome with breast augmentation surgery.My best advice: more communication. It is definitely worth spending more time (prior to the date of surgery) with your plastic surgeon to discuss further.  As you know, it will be important for many reasons, that you feel comfortable that you and your plastic surgeon are on the "same page" prior to proceeding.

Ultimately, careful communication of your goals (in my practice I prefer the use of goal pictures, direct examination/communication in front of a full-length mirror, in bra sizers, and computer imaging) as well as careful measurements (dimensional planning) will be critical.
Generally speaking, the best online advice I can give to ladies who are considering breast augmentation surgery (regarding breast implant size/profile selection) is:
1. Concentrate on choosing your plastic surgeon carefully. Concentrate on appropriate training, certification, and the ability of the plastic surgeon to achieve the results you are looking for. Ask to see lots of examples of his/her work.
2. Have a full discussion and communication regarding your desired goals with your plastic surgeon. This communication will be critical in determining breast implant size/type/profile will most likely help achieve your goals. 
In my practice, the use of photographs of “goal” pictures (and breasts that are too big or too small) is very helpful. For example, I have found that the use of words such as “natural” or "C or D cup” etc means different things to different people and therefore prove unhelpful.
Also, as you know, cup size varies depending on him who makes the bra; therefore, discussing desired cup size may also be inaccurate. Again, the use of computer imaging has been very helpful during the communication process, in our practice.
3. Once you feel you have communicated your goals clearly, allow your plastic surgeon to use his/her years of experience/judgment to choose the breast implant size/profile that will best meet your goals. Again, in my practice, this decision is usually made during surgery, after the use of temporary intraoperative sizers.
 I hope this helps. Best wishes for an outcome that you will be very pleased with. 

Thanks for your question and the photos. Given your height you do probably need a little more volume than most to get the look you want. 450CC HP would be way too big and round for you (based on your comments). I bet 375 or 400CC Moderate Plus Profile would be a better choice. As you increase the size (volume) you increase the weight. Your breast has definitely lost some elasticity over the years with children and age. I want patients to be happy. Needing a revision because of malposition and asymmetry is not "happy". I think the Vectra 3D imaging is the best tool to show patients what their expected outcome should look like. With regard to implant profiles, I give the analogy of shoes. If you are a size 8 for example you can wear tennis shoes (Classic profile), wedges (Moderate plus profile) or 4" heels (High profile). Hope this helps. Best of Luck!