500-600?? What is the difference size wise? (photo)

If you have almost 400cc already in place then you will barely notice a difference with a 500cc device.  That increase is essentially a third of a can of soda, which really is not much at all.  If you want to see a change, then I recommend being in the 550-600cc range to achieve the upper pole fullness you are looking for.  I hope this helps.

It was recently determined that a cup size difference is about 138 cc. However, there are other variables to consider such as projection. The dimensions of implants can be found online at the respective website of the implant manufacturers such as Allergan, Mentor, and Sientra.

Thank you for your question.  In general, we typically tell patients that every 150 cc to 200 cc is approximately one bra cup size.  Also please remember that the upper pole fullness achieved immediately after a larger implant is placed is mostly only temporary until the implant again settles as the skin and tissue accommodates the larger implant.  A pushup bra may again become necessary to achieve that upper pole fullness or cleavage long-term.  Please discuss these issues with your plastic surgeon prior to surgery.  Best wishes!

There is no accurate/reliable/predictable correlation between size/profile breast implant utilized and cup size achieved. For example, I do not think that the generalizations such as "200 cc equates to 1 cup" hold any validity or are helpful in any specific or practical way. 
Ultimately,  careful selection of your plastic surgeon and 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, and computer imaging) will be critical. Keep in mind as you are thinking about your goals that sometimes adjustment of the breast implant pockets (capsule adjustments) may be necessary to achieve the outcome you are looking for.
Generally speaking, the best online advice I can give to ladies who are considering revisionary breast augmentation surgery 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 “full breast” or "up a cup size” or " D or DD cup" etc means different things to different people and therefore prove unhelpful.
Also, as you know, cup size varies depending on 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 chosen plastic surgeon to work with you in determining the best plan to achieve your goals.
I hope this, and the attached link (dedicated to revisionary breast augmentation surgery concerns), helps. Best wishes.