Trying to decide between 365 cc or 400 cc, what should I do?

At size 36 A each 200 cc’s of implant corresponds
to 1 cup size change. 400 cc implants
would take you up to a size C. 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. There is no
significant difference between 365 and 400 cc implants.Best Wishes,Gary Horndeski, M.D.

Thank you for the question. Unfortunately, online consultants will not be able to provide you with specific enough advice to be truly helpful. Given your questions and concerns, you'll be best off spending additional time with your plastic surgeon communicating your goals carefully. Keep in mind, that there is no reliable correlation between the breast implant size/profile use and specific cup size achieved.
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'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  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 him who makes the bra; therefore, discussing desired cup  size may also be inaccurate.
 The use of computer imaging technology may also be very helpful during this communication process.

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, dedicated to more "natural" looks ) help.

This is always a difficult decision for some. In my opinion, the best thing to do is have a thorough sizing session. I provide my patients with a range of about 3-4 implants that are appropriate for their specific measurements. I then have them try these implants on in a special sizing bra. With this process, my patients have been able to choose their own implants. I have found this to be the best method for implant sizing. Be sure to see a board certified PS in your area. They should be willing to spend the time with you doing this. Best of luck!