Is there a noticeable visual difference between 455 and 480cc UHP Mentor?

There is only a subtle difference between the two breast implant sizes that you mention but if you are increasing your size, I would consider the larger of the two. My experience is that when someone is choosing between two sizes AND they are in the process of exchanging for a larger implant, they are usually happier with the larger size. Talk with your plastic surgeon, though, and explain exactly what you desire. Everyone is different and your results need to be customized to your goals and body type. Good luck!

A small change in CC's may not be drastic enough to notice a significant size increase. Depending on the reason for the breast revision determines the sizing outcome. However, there are no guarantees with size predictions for revisions. Initially, if a woman wears a size 36 AB bra and would like to be a C cup, which is the average size that women wear and the average size bra that is sold, she needs a volume of approximately 350 to 390 cc to make that change. This becomes less if she's wearing a 34 bra, because it has a smaller strap size and the cups have a smaller diameter. A smaller diameter implant would then be a volume of approximately 300 to 350 cc. In the same way if she was more petite, maybe a double zero or size one and wore a 32 AB bra, then to become a 32C cup she would only require about 250 to 300 cc. This is a general number, and of course there are other factors that will affect this. 
Other factors which contribute to the outcome are #size, #shape, and #profile.  The #profile is determined by the amount of #projection versus roundness that the you desire, as well as the #size of the implant and size of your chest. Also, the placement or incision location will also have an effect on profile. Another element to a satisfying result of your #augmentation is realistic #expectations.#Shaped implants are all #textured and should not rotate when used properly. In my practice, about 20% of the patients benefit from shaped implants. Your Plastic Surgeon needs to measure you and determine the best shape and size of any implants that are used.

No. The difference should be minimal. I think that would be unlikely to notice a size difference.

Nope. 25cc is less than one ounce. Even those of us who do this surgery every day would be hard-pressed to see that little of a size difference. At the end of the day, all patients must rely on their plastic surgeon to make the final decision on implant size depending upon the needs at the time of surgery. Best of luck with your surgery.

Thank you for the question.  Exactly how much larger you can achieve during the revisionary breast surgery will depend mainly on your physical examination; for example, for petite patients a 25 cc difference can be slightly noticeable; for larger patients, this difference may  not be clinically noticeable.
 
Ultimately, careful communication of your goals (in my practice I prefer the use of goal pictures, direct examination/communication in front of a full-length mirror, and computer imaging) will be critical. 
Generally speaking, the best online advice I can give to ladies who are considering 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 "D or DD cup” or "one cup size increase" or "noticeable change" etc means different things to different people and therefore prove unhelpful.
Also, as you know, cup size varies depending on 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). Viewing the patient's chest wall in the upright and supine positions, with temporary sizes in place, help select the best breast implant size/profile for the specific patient.
I hope this, and the attached link (dedicated to revisionary breast augmentation surgery concerns), helps. Best wishes.