Will Decreased Breast Implant Projection Produce Significant Downsizing Results?

Hi there-
I think you are being too analytical about the process- in the final analysis, you are trying to achieve a certain improvement in your body contour, not a certain number on your implants or letter on your bra, right? The major concern in your situation is that it is not possible to take into consideration the elasticity of your tissues until the force of the implant is in place, so choosing an implant based SOLELY on the numbers is an imperfect science, and I would be worried that you still won't be as happy as you could be.
I would focus more on communicating your goals for appearance effectively to your surgeon and trust him/her to use their best judgement in the decision making process.

The almost 2 cm difference in projection will cause a significant decrease in the appearance of the size of your breasts. The moderate profile is about the same diameter as your original implants (just a tad narrower) so you will still have about the size across each breast. It is important to choose an implant that compliments the width of your chest wall to be sure that it is not too narrow for a "fake" look or too wide where the implant appears to be falling too far toward the armpit. 

Determining implant size is very difficult. However, based on the information, it seems that you will see a significant change in size and projection. Mentor is a very high quality implant and use it for many of my patients. I usually use moderate to moderate plus profile implants to achieve a more natural look. Internally your anatomy is very different and depending on whether your chest is convexed or concaved, the projection will make a difference. 

I recommend finding before and after photos of what you would like to achieve and show it to your surgeon so that you have a good understanding of the look you want. Make sure you have a board certified plastic surgeon performing your surgery to acheive the best and safest possible results. For more information regarding removing and replacing breast implants, check out and compare before and after photos of patients who have downsized as well. Good luck.