What size at an estimate would I be going from a 36DD with 500cc to 800cc?

Thank you for the question.   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 of "200 cc equates to 1 cup" hold any validity or are helpful in any specific or practical way.  In my practice, I ask patients not to communicate their goals, or evaluate the outcome of the procedure performed, based on cup size references.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.
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 “natural” or "up a cup size or two” or "G 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 larger   breast augmentation surgery concerns), helps. Best wishes.

Hi Lauren,It is very common for patients to want an idea of the cup size that they are likely to achieve, but it is notoriously difficult.  Unfortunately, bra cup size is all that we have to go on, so it is natural for us to talk about breast size in this way, but it is very difficult to predict the final cup size.You can get an idea of what the extra 300cc would feel like in your bra by trying on a 300cc sizer in the clinic.  However, it is also important to consider the dimensions of the implant as this is often overlooked by patients.  If you are going from 500cc to 800cc but keeping the same shape and profile of implant, then it will be bigger in every dimension (width and projection). If you are changing the shape and/or profile of the implant (ie going from teardrop to round or from high to extra high), then the extra volume may be more obvious in the projection (maintaining a similar width) and this will have more of an effect.I have just read this back to myself and I know it might sound a bit confusing, but the bottom line is that it is difficult to predict cup size and you need to choose an implant that will fit the dimensions of your breast and give you the sort of look you are trying to achieve.  Good luck!