32AA. 5ft 5in 120lbs. Want 400cc implants but PS is trying to talk me down. Want a second opinion. (photos)

The best way to help you make an informed, sophisticated and personalized decision that is right for you is to have me examine you and review your goals. While you have several views depicting your body habitus, there is no substitute for a physician-patient relationship. Since I am in Mentor, I invite you to call my office for a full evaluation. You are best served if your personal augmentation goals are in sync with the specifications of your physical examination, aligning you with the implant that works for you. We will work through this together! I look forward to our collaboration! 

Dear 32AAnna,breast implant type and sizing selection is a complicated process and requires a detailed consultation that includes a discussion of your goals, a detailed examination, and a lengthy discussion. But the decision will always start and end with the patient. When it comes to sizing, we have all of our patients find 3 photos of their desired breast size. We ask for naked breast photos because clothing can obscure the true size (push up bras). Next, we consult with patients and go over the photos and take detailed breast measurements during a physical exam. Next, we using a sizing algorithm to determine a range of implants that will work based on the exam and the measurements.Lastly, during the operation, we use silicone sizers in the operating room to see how the size actually looks in the breast. We sit the patient up in the operating room, while asleep of course, and compare the sizer result with their desired look photos. If it is too small, we start the process over with a slightly larger implant. We don't stop until we get the perfect match.Of all of my breast augmentation patients, every one of them has been happy with their size due to this detailed and meticulous process. You don't want to invest time and money into a result that is either too big or too small.You should discuss your concerns with a board-certified plastic surgeon and make sure that your surgeon understands your goals.Daniel Barrett, MD, MHA, MS 
Certified, American Board of Plastic Surgery  
Member, Am. Society of Plastic Surgery

Patients often think in terms of cup size when considering augmentation. Unfortunately, devices are sized in terms of milliliters (cc) of volume. This can lead to some confusion when sizing. Additionally, it is important to remember that cup size itself is not standardized with variations from one manufacturer to another. Unfortunately, as many women can attest their cup size in an industry leader such as VS is not necessarily transferable to another brand.
Another point which is often under appreciated is that of anatomy and starting point. Any implant will add volume to the volume which is already present. The implant is additive. A particular volume will not necessarily confer the same cup size to different patients (often times it will not even confer the same cup size to different breasts in the same individual...remember they are "sisters" not "twins"). 
A general rule of thumb is that 125cc can represent somewhere between 1/2 to a full cup size increase. Smaller volume differentials (25-50cc) are typically less consequential representing a volume change of less than a shot glass. However, I have found these numbers, at least anecdotally, to be of little help. Patients often present with notions/goals which do not correlate with these sorts of sterile volumetric assessments.
When sizing patients, there are a number of useful tools including:
-3D imaging (has the added benefit of offering a volumetric analysis of the pre-operative breast)
-Breast sizers (rice bags)
-Goal photos
I also recommend that patients commit to a particular look rather than a cup size. Once a patient settles on a look that pleases them the overall cup size increase becomes less relevant.The key to obtaining a natural result is to stay within the parameters defined by your BWD. This will ensure that you avoid the dreaded "fake" look. 
The question of "too big" or "large enough" is a relative question. The safest approach is to stay within the boundaries of your BWD. Beyond that, the choice is yours. Based upon your photos alone, I would typically recommend conservative sizing as larger implants on smaller framed individuals are often considered the definition of "fake." This stems from the fact that there are not many small framed individuals with large breasts that have not undergone augmentation. That being said, if you are amenable to a less "natural" result, you should be able to proceed with a more dramatic augmentation. Another option is to consider a higher profile device which will allow a greater amount of volume for a given BWD or breast foot print. The excess volume equate to greater projection or, as you said, "bustiness."
As always, discuss your concerns with a board certified plastic surgeon (ABPS).