How much difference is there between 400cc and 525cc? (photo)

Thank you for the question and picture. The operation you are considering is not necessarily straightforward;  experience does matter when it comes to achieving an outcome that you will be pleased with.Generally speaking, patients undergoing the breast augmentation/lifting combination operation should understand that it is significantly more complex than breast augmentation surgery only and that it is associated with will a significantly higher risk of complications and need for additional surgery.  Again, it will be important that you educate yourself regarding the pros/cons/risks/complications associated with breast augmentation/lifting surgery.
 Remember, that during breast lifting surgery, some skin is removed, thereby limiting the "space" available for breast implants. On the one hand, breast augmentation surgery is expanding the breast skin “envelope” while breast lifting is (by definition) tightening up the breast skin envelope. These 2 forces are counteracting each other. Therefore, it becomes important to remove the appropriate amount of breast skin and to use the appropriate size/profile of breast implants to balance these 2 forces appropriately and to allow for achievement of the patient's goals while minimizing risks of complications. 
Generally speaking, the best online advice I can give to ladies who are considering breast augmentation/lifting or revisionary breast 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. For example, I have found that the use of words such as “natural” or "C or D cup" etc means different things to different people and therefore prove unhelpful.
Also, as you know, cup size varies depending on him who makes the bra; therefore, discussing desired cup size may also be inaccurate. Again, the use of computer imaging has been very helpful during the communication process, in our practice.
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 (read about the tailor tacking technique), after the use of temporary intraoperative sizers.
I hope this (and the attached link, dedicated to breast augmentation/lifting surgery concerns) helps.  You will find a separate page, on the same website, dedicated to revisionary breast surgery concerns. Best wishes for an outcome that you will be very pleased with.  

Remember that the heavier the implants the more likely you might get early ptosis recurrence. It may also depend upon the dimensions of your chest and the size of the implants.