I have answered a similar question for another woman; my answer can be found under my profile by clicking on breast implants and reviewing the answer to the question "Breast Implant Sizes.".
Please realize that the 550-600cc implant size you anticipated is only 100-200cc different from what your consulting doctor recommended. Perhaps he is way off base and not even American Board of Plastic Surgery certified; perhaps he is properly-board-certified, well-trained, experienced, and is recommending 3-6 ounces more enlargement per side than you anticipated. (This amount is 1/4 to 1/2 of a can of soda! Put 3 ounces of water in a bowl and ask yourself if you think you could see a difference in breast size if that amount were added to your present size--or your "perfect" size. Do the same with 6 ounces. You'll see that it's either "not too much" or "too much."
Particularly with under-the-muscle placement, I typically add 100cc to whatever the patient chooses (when they choose 600cc; for a choice of 300cc, I might add about 50cc) in order to achieve the "look" the patient wants when sizing with implants in a bra. Sizing in a brassiere is entirely different than what a patient experiences when the implants are entirely covered by muscular tissue! I know this from multiple patients who chose a specific size, after which I dutifully placed exactly-the-requested-size in the operating room, only to have them react with "You put in the wrong ones--they're too small!" in the recovery room or the next-day recheck! So I quickly learned to add a sliding scale "fudge factor" that makes more patients feel I got it "right on."
The issue is further complicated by the fact that implants come in not only multiple volumes, but also three different profiles--moderate, moderate plus, and high profile. The differences are: narrower base width and greater height (projection) for the high profile implant, compared to wider base and lower height (projection) for the moderate profile implant. (Moderate plus is in-between). I choose profile based on patient measurements, requests, and anatomy. Your own anticipated implant choice may have included these variables, but not the 25 years of experience and the thousands of breast augmentation patients I have discussed this very issue with at length. And I still don't ALWAYS get it right; but since I don't charge a surgeon's fee for a revision (and the patient has to pay for the new implants, OR, and anesthesia), neither I nor my patients want to do that very often! Either I learn or I my practice doesn't thrive.
To sum up, 700-800cc may be a tad too much, or it might be spot on! Did you bring photos of what you consider to be breast sizes you find attractive to your consultation? Is your doctor American Board of Plastic Surgery certified? Does he have years of experience? Does he do primarily breast surgery? cosmetic surgery? reconstructive surgery? Or is he a Dermatologist or (facial) plastic surgeon?
You are wise to ask these questions now. Try on implants in a bra and stretch top when sizing, and DON'T look at the numbers. Ask the doctor if he or she has their own "fudge factor" or if they put in exactly what you choose. Ask what their redo policy is and who pays for what. I've written more on this topic, and you can find before and after breast photographs on our website photo gallery with the patient data and (accurate) implant sizes and profiles. I hope this helps you! Best wishes!