Will 400cc high profile implants be too big? I had 250cc implants 6 weeks ago and they are without doubt too small. (Photo)

Anatomical measurements and a physical exam will be necessary to determine if a larger implant will be suitable for you.  Tissue quality and base width are two determining factors.  400 cc's is larger but you may do well with them.  Good luck. 

Thank you for the question and pictures.    Ultimately, careful communication of your goals (in my practice I prefer the use of goal pictures and direct examination/communication in front of a full-length mirror) will be critical.
Generally speaking, the best online advice I can give to ladies who are considering breast augmentation surgery  or 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 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 "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.
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 revisionary breast surgery concerns), helps.

Upon
examination of your photographs, it appears that your breasts do seem to fit
your body type. Your body type looks to
be thin with not a lot of subcutaneous fat or breast tissue. In a thin patient with a minimal amount of
subcutaneous tissue, you should not go too big.
I believe that your results at this juncture looks natural. I believe a 400 or especially a 500 cc
implant will look extremely artificial in your body.