Is a 510cc saline implant considered large for an extremely active person? (Photo)

At size 36 each 200 cc’s of implant corresponds to 1 cup
size change. From this, you can compute
the volume required to achieve your desired goal. I always recommend small round textured
silicone gel implants placed retro-pectoral since they look and feel more
natural, are more stable, less likely to ripple or have complications needing
revision. Implant profile is irrelevant
in the retro-pectoral position since the muscle compresses it. Large implants such as 510 cc’s will extrude
inferiorly and laterally requiring revision.
Unfortunately, your photograph does not show your breasts directly so I
cannot access if you have drooping. If
you have ptosis a simultaneous lift may be helpful to you.Best Wishes,Gary Horndeski, M.D.

There is a clear connection between large size (350cc or bigger) and complications. Women who get sizes that are in the 400 to 500 cc range enjoy these for a while but often see that the weight, the bottoming out, possible capsule formation, and an overall heavy look is not so desirable. I alway counsel my patients about size and using Vectra 3D imaging show them the potential that is in store for them. Patients always have the final say, but I really try hard to counsel a more reasonable size for them. 

Thank you for the question and picture.  However, despite good intentions, online consultants will not be able to provide you with  meaningful specific advice.  Ultimately, in person consultation with well experienced board-certified plastic surgeons will be necessary. Careful measurements, dimensional planning, and careful communication will be key.
Generally speaking, the best online advice I can give to ladies who are considering revisionary 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're 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 which operation and/or 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 "C or D 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.  The use of computer imaging may be very helpful during this communication phase.
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.
I hope this, and the attached link, helps.

I think that you need to be evaluated in person to determine if the implant you want is the appropriate size for you.  Answering that here without an exam is impossible.

The difference between 475cc's and 510cc's will not be noticeable for you. However, if your base width is only 12.5 and 13cm a high profile implant still warrants consideration. The moderate profile implant is going to be much wider than what you have in and you will have more breast laterally (on the sides) than you are used to. So it's not your volume choice rather your choice of profile.