5'9, 155, going with 425cc silicon, under the muscle, HELP! (photos)

425. Cc implants will not be too large.  If you were choosing a size that was unreasonable, I would not be shy about letting you know.  As long as you're the Nader 500 cc's you will be fine.

Hello,You need to use a tight, unpadded bra and place 400 cc implants into your bra, place a tight shirt on, and look in the mirror. This will roughly replicate what 425 cc will look like. This is called sizing.  This is the only way you can get your answer: from you. You are asking a question of opinion, something surgeons don't delve into. Our job is to make sure you have the anatomic capacity for any given implant, not whether it is 'proportional'. Best of luck!

Hello and thank you for your question. You are a great candidate for a breast
augmentation.  The size, profile, and shape of the implant is based on your desired
breast size/shape, your chest wall measurements, and soft tissue
quality.  This decision should be based on a detailed discussion
with equal input from both you and your surgeon.  This entire surgery can be performed with a
small incision technique.  Make sure you specifically look
at before and after pictures of real patients who have had this surgery
performed by your surgeon and evaluate their results.  
Best wishes and good luck.
Richard G. Reish, M.D.
Harvard-trained plastic surgeon

OMG, these are questions, sentiments, factors, and doubts to be considered, deliberated, and resolved in front of a full length mirror with your surgeon in the consultation room long before a scalpel ever touches your skin.  Such individualized, personal concerns can never be appropriately or professionally addressed online even by expert surgeons who haven't the information provided by meeting you in person, understanding your needs, physically examining you, and then considering available possibilities to achieve your desired outcome.Return to your surgeon with your important questions.  Minimizing the chance of (unpleasant) surprises after surgery is a function of preparation before surgery.

It's normal to be nervous about your implant selection prior to surgery.  Hopefully you had the opportunity to try on sizers so you could see what your end result would be.  I would suggest calling your PS office and speaking with your coordinator.  Often times, they can ease your anxiety and assure you that you will be very happy.  Good luck!