The two implants you refer to have a different base diameter and projection, meaning that if you place the two next to each other on a flat surface (assuming equal volumes), one will be narrower and have a higher peak, while the other will create a larger footprint on the table but have a lower peak.
Having said all of that, I think it is a tremendous mistake for patients to get too involved in the implant selection process, as there is no way for you to understand the tissue/implant interactions that can only be understood by ANYONE at the time of surgery.
One of the things I find most interesting is the amount of misinformation the average patient must sift through when researching breast augmentation surgery. In particular, I think that many patients become overwhelmed with implant choices and the abundance of information about these options available on the Web.
This is complicated once they contact a surgeon or two for information about the implants, and which is most likely to give them the result they desire. Somewhere along the way, opinions expressed by a surgeon are perceived as fact by a prospective patient (because of the surgeon's reputation or the apparent strength of his/her opinion), who then becomes more confused when she hears a differing opinion.
This leads to ridiculously technical questions being posted on sites like RealSelf and others, such as:
"I am 5'5", 125 lbs, my measurements are 34, 22, 36. I have had 3 babies, all by C-section, and I breast fed two of them. My breasts sag a little, but not as much as some women I have seen. I want to have a full C-cup breast. Should I get 325 cc Allergan 410 style implants, or Mentor 350 cc Moderate profile implants. Projection is more important to me than a natural shape..."
Every time I get one of these over-thought questions, I always think the same thing... ???????
Let's take a big step back from the trees here and take a look at the forrest in front of us, shall we?
Fundamentally, the reason any woman seeks breast augmentation is because she wants to achieve a certain appearance, right? Let's repeat that- to achieve a certain appearance. NOT a certain bra size, or a certain implant volume, or even a certain implant type. When you first stared to think you might want an augmentation, you didn't think, "I would like it if I could have 350cc implants"... You probably thought, "I would love to look like that (after admiring another woman's breasts)..."
So if we can agree that what you are really after is an appearance you would be happier with (as I always tell my patients), let's make the desired appearance the focus of our communications...Let us both ignore bra sizes (which are not standardized and the choice of which is very arbitrary) and implant types/sizes (for now)... Let's first understand what you want to look like. I think you would agree that if we are able to make you look the way you wanted to look, the letter on your bra and the number on your implant is lees important, right? Help me understand what you want to look like, and I can give you a very accurate recommendation of options for achieving that appearance -- provided a careful physical examination has also occurred.
Why is the exam so critical? After all, can't we just put small implants in women who want small breasts and larger implants into those who want larger ones?
The exam is critical, because for any one particular woman, there are only a few good choices of implants available, regardless of her goals, and these options are arrived at by taking careful stock of her breast tissue, skin, and frame. In other words, your anatomy will, to a large extent, help us understand the implant options that would make you look the best. This is the "One Right Result" concept. The taking of these measurements is so important, I do it myself every time, and based on these measurements and my patient's goals, then make recommendations regarding the implant options available to her (as these options would be different for different women).
While (as with any aesthetic procedure) no guarantee of outcome can be given, you are much more likely to achieve your desired outcome if you focus on communicating your desired appearance successfully with a skilled and experienced, Board Certified Plastic Surgeon than by over-researching the implants and micro-managing the details of the surgery. In fact, I can think of no better way for you to increase the odds of you ending up dissatisfied.
So don't over-think it. Think carefully about the appearance you want, communicate it carefully to your surgeon (using photos if possible), and make sure that the implant choice arrived at by the two of you together is based on both your anatomy and your goal. You'll be happier and the process will be less stressful!