34A wanting to be a 34D. Is this too big for being 5'11"? (photos)

Thank you for the question.  Despite your good description of body type and goals, online consultants will not be able to provide you with specific enough advice to be truly helpful.  Ultimately, careful selection of 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, in bra sizers, and computer imaging)  as well as careful measurements (dimensional planning) will be critical.
 
  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 "full C or D cup" or "too big" 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 sizing concerns) helps. You will find a separate page, on the same website, dedicated to athletic patients ("patients in action")  as well. Best wishes for an outcome that you will be very pleased with.

There are many different factors that are involved in making this decision that have already been well expressed by the other plastic surgeons who have commented.  Your desired size and the measurements of your current breast base diameter and tissue characteristics are the most important.  There are many ways to help you visualize what the outcome will look like from 3D imaging to stuffing your bra.  In the end, this should be a decision made between you and your plastic surgeon, it is very difficult to answer with meeting you, talking to you in person to hear your concerns and examining your breasts.  Having said that, at 5'11" and after seeing your photographs, a 500 cc implant doesn't sound out of the question.