I'm an AA-Acup. What size cup will I be with 600cc implants?

I agree with the other docs who have answered already. 600cc is a very generous implant on anyone. You sound to be of a slender build. Just keep in mind that women are best served when the implant selected fits within their frame. And, large implants on a slim frame tend not to have much camouflage and so the 'falseness' of the result can be very apparent (more so than with a more conservative volume). I feel that most women's tissue and skin wears better over time with a more conservative breast augmentation. These are just things to keep in mind. I encourage my patients to read as much as possible when considering the implant chosen. Please don't consider bra size as your most important goal. Katy Perry does have a very natural and voluptuous look but if your frame is very different from her's, you will feel that you have a very different result.  I have attached a blog article I wrote for my group that covers a lot of topics in breast augmentation.

Thank you for the question. There is no accurate/reliable/predictable correlation between size/profile breast implant utilized and cup size achieved. Ultimately, 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. Given that your surgery is coming up soon, I would suggest that you schedule additional time to spend with your plastic surgeon communicating your goals, preferably prior to the date of surgery.
Generally speaking, the best online advice I can give to ladies who are considering breast augmentation surgery ( regarding breast implant 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. For example, I have found that the use of words such as “natural” or "C or D cup” 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. Again, the use of computer imaging has been very helpful during the communication process, in our practice.
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.