Implant exchange from 450cc's to 650cc's

In my opinion, your desire for a fuller look likely can be met without going larger, but going to a plastic surgeon that specializes in breast surgery.  Going larger as you have stated will result in complications most likely as you age and gravity takes its toll. 

450
cc implants weigh approximately 1 lb each and 650 cc implants weigh about ½ lb
more. The additional weight will cause skin
stretching resulting in inferior and lateral displacement requiring
revision. The other alternative is
reshaping your existing breast tissue with a new technique called The Mini
Ultimate Breast LiftTM. Using
only a circumareola incision it is possible to create upper pole fullness,
elevate them higher on the chest wall and more medial to increase your
cleavage. Aligning the areola, breast
tissue and implant over the bony prominence of the chest wall maximizes
anterior projection without changing out the implants. This may give you the look you desire while
avoiding the ugly vertical scars of the traditional technique, maintaining
nipple sensation and the ability to breast feed. Best Wishes,Gary Horndeski, M.D.

Without an exam it is impossible to determine if larger implants will cause greater problems for your particular case, but in general, larger implants do cause more problems.  Larger implants are heavy and this will result in more droopiness and stretching of the skin which will make the implants more visible.  But you're right, you will have to weigh those risks with you're desired look.  Make sure to discuss your concerns with a board-certified plastic surgeon.

and if being the cup of your desires will have a positive impact in your life, then consider it and accept the long term risks that some doctors like to scare patients with in order to get them to pick a smaller size.  Life is about living and trying to minimize regrets.  Will having more surgery in the future (lift and possible downsize) be acceptable to have the cup of your dreams?  Only you can make that decision.

Larger implants can lead to bigger problems due to the weight. It can lead to bottoming out or early sagging of the breast as well.

Everything you say is true, very large implants are prone to thinning and show through ripples, and sagging. You could easily go up the 200ccs. Is it worth the risk? Hard to answer this one, but your might try on clothing with the extra fill and see if the feel is right for you.

Thank you for your question. Larger implants can increase the incidence of late complication. If you have a small amount of breast tissue to begin with, a larger implant can stretch that tissue out to reveal ripples, distort the pocket, and cause malposition. Discuss this with your Board Certified Plastic Surgeon to see what the limits of your anatomy might be. I hope this was helpful.

A very thoughtful question and I am glad you are addressing it. We can't know the future, but implants of that size certainly can cause more problems as you age, especially if your tissues are thin. Go ahead only if you are willing to accept these risks.