Is 425cc Too Big for B Cups with C Cup As Goal Size?

No one can answer this question for you.
Your best option, in my opinion is to try on sizers, give your input, and take responsibility for your decision. What works for your lifestyle now may not be desireable 5 years from now and that means either larger or smaller. Your surgeon, is making a recommendation based on his/her 20 year experience. He/she likely knows that the average person desires a larger implants after surgery. However, you may not be the average person and he/she cannot read your mind. Express your thoughts, desires, and goals.

For your body and frame that does sound a bit too big. But it is really hard to say just from a bunch of numbers. One would need to see you and do base diameter measurements to see how wide your chest is.
Also what you can do is to perform the rice test to see what 425 cc looks like on you. Here is a journal entry on the rice test. http://www.feplasticsurgery.com/journal/orange-county-breast-augmentation-sizing/66/
Hope this helps you out.

Hi,
With your height and weight, and if you are truly a B cup, 425 cc implants will almost certainly make you larger than a C cup. That being said, you will have a very full, round look - this may be the look you're going for. If it's not, and you truly only want to be a C cup, you may wish to seek the opinion of another board certified plastic surgeon.
Hope this helps. Best of luck.

You and your surgeon should work together to decide on the implant size. It's your body and your decision. On the other hand, pictures aren't much help either. Our process is to have the patient try implants on in a bra of the size they want. It's not a perfect process but at least you have a good idea of what you are getting. When you say you are scared to death they are too big, then they are too big.

Unfortunately, there is not a general rule of thumb or objective criteria to implant selection.
Your plastic surgeon will perform several measurements of your chest wall and breast anatomy and determine a range of implants that both fit your chest wall and reach your desired goals.
The next step is to try on this range of implants in the office with your doctor.   The key to this success is showing your surgeon the body proportion you desire with a bra sizer and allowing your surgeon to guide you to the right implant.   It will be much easier to communicate in implant cc's than cup size when determining the appropriate implant for you.
I wish you a safe recovery and fantastic result.
Dr. Gill