Thank you for your question and photos. An examination in person would be required to properly evaluate you and make specific recommendations. That said, based on your photos and dimensions, the 450 is almost certainly going to give you an exaggerated unnatural look which you would like to avoid. You appear to have generous breasts and if you are looking for a rounder fuller look and Moderate (classic) or lower profile implant should suffice. Volume (300 versus 400), is far less significant than implant width and projection. Implant width is similar to shoe size. The implant literally needs to fit into your breast and chest. The 450 implant may well “fit” your breast, but the volume and projection are what will determine the “look” you want, similar to the style or type of shoe you would select. It is true that for a given volume a high profile implant will have a narrower diameter, and it is also true that a person such as you with a petite frame and full breasts should require a wider diameter implant to enhance fullness and roundness. Other considerations such as saline versus silicone are also important, as are "round" versus "anatomical" or "form stable" or "shaped", smooth surface versus textured, and softer versus firmer with the different levels of gel cohesivity. The term “natural” can mean different things to different people and the profile of the implant does not necessarily determine that. You can certainly achieve a “natural” appearing result with a high profile implant if properly selected, but as a rule, the larger the implant and the higher the profile, and certainly if the implant is positioned too high, the greater the chances you will look “augmented” because of exaggerated upper pole fullness or convexity. In my practice, besides a thorough interview process and physical examination with careful measurements, we use on lay sizers within an unpadded bra to help you understand what you are likely to look like in a bra, bathing suit, or T-shirt with a given size implant. In addition, and this is critical, we ask all of our patients to provide us with photos of their desired final look, with images of women’s breasts that most closely resemble the look they are trying to achieve. This serves as a visual guide that thankfully rarely leads us astray. The most common reason for patient disappointment after breast augmentation is size-too big or not big enough. This algorithm which we have been employing for over thirty years has proven to be very successful. Because all of these factors can leave you quite confused, it is crucial that you select an experienced board certified plastic surgeon whose aesthetics align with your own, and with whom you feel comfortable. Don't be reluctant to seek a second or even third opinion if necessary to be sure and feel confident about moving forward with scheduling surgery. Expressing your desired cup size is notoriously inaccurate, and final breast size is the most common reason for patient disappointment after breast augmentation, either too big or not big enough. Take your time, do your research. Best of luck to you.