Though other colleagues may specify a different number, I have reliably (over 25 years) used the "rule of thumb" that 250cc equals about one cup size. Thus, you would be adding just over 1 1/2 cup sizes to whatever breast tissue you already have. At "full A to small B" you would end up with a full C to small D. This can be confirmed to some degree by trying on implants in a bra and stretchy top, but I have also found (the hard way) that 50-100cc needs to be added to the patient's bra-sizing choice to give a similar look when inside the patient's body, under her muscle.
(BTW, this is one reason why so many women end up being "too small" when everything is healed and settled--their surgeon used the patient's choice without realizing that this yields consistently slightly-too-small results!)
Based on the information you have provided, I suspect that even the 425cc implants will be a bit small for your wishes. But, trying implants on in a bra and top, as well as bringing photographs of desired breast size results for your surgeon to discuss with you, will help you and your surgeon choose proper implant size and profile to give you a result you can both be happy with, and a decreased likelihood of needing re-operation for larger implants or breast lift scars.
Of course, physical examination of your breasts, and careful measurements will contribute to the decision-making process, particularly when the implant volume is decided upon, and then the profile of the implants chosen to most precisely correspond to your breast base (or more accurately, your breast pocket's) diameter.
There is a natural tendency for surgeons to be reluctant to use larg(er) implants, especially in petite women. There is a natural tendency for women to be reluctant to ask for the implant size they really want (peer pressure, fear of [too much] visibility, modesty, fear that bigger breasts may make them look fat, etc.). Yet, 6 months after breast augmentation, when all of the "worried-about" social situations have been successfully overcome, when "nobody noticed" unless the patient wears a revealing top or a tight bathing suit, and when the patient finally realizes that nobody really "cares" how big or small her breasts are and that size and perkiness was really HER issue much more than anyone else's, all too many patients sheepishly admit they wish they had gone just a little bit bigger!
As Doctor "Bones" McCoy of Star Trek fame might have said, "Dammit Jim, I'm a doctor, not a psychologist!" Yet as plastic surgeons striving to make out patients happy for the long term, being aware of these common, if not quite universal, tendencies helps us to advise our patients properly. Simply acting as surgical technicians is not enough. We have done this operation hundreds, if not thousands, of times. If we see our patients in follow-up visits over many months and even years, we ultimately "find out" what they really think about how they look for the long term! That helps bring some experience to the decision-making process, while fully respecting each woman's right to decide what she wants for herself. It's NOT the surgeon's job to "dictate" but to provide expert assessment of each woman's unique anatomy and measurements, LISTEN carefully to her wishes and goals, and then DO OUR BEST to achieve that in the operating room with the highest technical expertise. If not anatomically possible, then we owe it to be honest with our patients rather than just proceed with what WE think is best.
Ultimately, it's your body, and your choice. Get several opinions from experienced ABPS-certified plastic surgeons (not just "cosmetic surgeons" with bogus board-certification, and not fully trained in plastic surgery). You might just find that 450-500cc is closer to what you need to achieve your goals! Best wishes!