Left: 470 right: 450. Too big or just right?

Your implant sizes that you mentioned are indeed fairly large for your frame and I find that doing sizing with implants placed in a bra works very well for women with very little tissue, but can be inaccurate in women who have as much tissue as you do. Personally, I would recommend that you find a surgeon who will use intraoperative sizing to pick the best implant size within a range that you determine beforehand with your surgeon. I like patients to bring in pictures of their ideal breast, preferably pictures of someone who is close to their size and shape.Going too large is very difficult to correct. It is always easier to increase the implant size later if you wish to go larger. 

Based on your frame, you have chosen large implants that may feel heavy and tend to sag over time. I would suggest going back and trying on sizes a little smaller that will fit you better. Long term, you will have better results with somewhat smaller implants.

...then they probably are. Being made larger than you wish is a bell you cannot unring, unless you have revision surgery. Ending up slightly smaller than you expected can always be enhanced with the right bra, etc. To be honest, for your dimensions, the implants you have selected are indeed fairly large. Form the standpoint of aesthetics, it's hard to "argue" with what you like. From your photos, you need to probably have at least a dual plane augmentation to achieve the proper degree of lift. Continue the discussions with your plastic surgeon. If in doubt, consider a second opinion. Best of luck to you.