Should I get 400cc or 450cc? Is there a big difference?

You should try sizers on to determine which is the best for your personal perception of size.  If you want to be a D, and you choose the smaller size, you will most likely be disappointed later.

Don't get caught up in fretting over actual number of cc's of your implants. There are so many other factors involved, like your height, weight, body type, size of your breasts and Breast diameter. I ask patients to show me photos of breasts they desire, a good starting point. I then use various sized implant sizers with bras and a T shirt to allow the patient to see what she likes. This narrows it down further, and lots of conversation with the patient gives me an excellent idea regarding implant size. Seek out a board certified plastic surgeon to help you decide.

Without knowing your particular body size and shape it is impossible to answer your question. In general a 50cc volume difference can make a significant difference in perception. trying on sizers is the best way to determine how your body will look with a certain size and profile device.

There will not be a noticeable difference in clothing with 50 cc's.  It is much better to accurately discuss implant volume and projection with an in office exam and detailed measurements. In order to make an accurate size recommendation, I would need to assess your chest wall and breast mound measurements/characteristics. I use these measurements to help me during the sizing process to guide you to a safe result for your chest wall and just as important, one that meets your end desires.The next step is to try on this range of implants in the office with your doctor. The key to this success is showing your surgeon the body proportion you desire with a bra sizer and allowing your surgeon to guide you to the right implant. It will be much easier to communicate in implant cc's than cup size when determining the appropriate implant for you during the sizing process. In addition, review of photos and use of rice bags can be very helpful to the patient and surgeon in achieving a safe and happy result. Close intereaction and involvement from your surgeon during this process can help alleviate the anxiety and fears of choosing the right size. I wish you a safe recovery and fantastic result.Dr. Gill

I can't tell you which implant size you should get, but I can tell you that when my patients come in, they always try on our impant sizers to find the shape and size that best fits their body and lifestyle.  I encourage them to come in for an additional sizing appointment if they are undecided.  It's also quite common for them to bring in a friend or significant other - as well as take pictures of themselves with the sizers - to help them decide. 

Thank you for the question. Depending on a specific woman's anatomy and goals ( in regards to outcome achieved with breast augmentation surgery), 50 cc may make a “big difference”.  For example, for a petite patient striving to achieve a relatively “modest” outcome, 50 cc of a larger volume implant may be very noticeable. Generally speaking, the best online advice I can give to ladies who are considering breast augmentation surgery (regarding breast implant type/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. I have found that the use of words such as  “natural” or "small D cup" or  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.
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, and the attached link (dedicated to breast augmentation surgery concerns), helps.  Best wishes.