Time for revision! 700cc or 650cc's? Will 50cc's make a big difference? What bra size could this probably get me to?

 Thank you for the question. 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.  Online consultants will not be able to help you select between the two sizes you are considering; in my practice, this is most often a intraoperative decision made based on visualization with temporary sizers, careful measurements (dimensional planning) and after careful consideration of the patient's goals.
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 fake look” 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 helps. Best wishes.

I don't think 50cc would make a difference. The implants are not that much different. Best wishes.