Upgrading from 325cc to 400-450cc Breast Implants?

In my opinion, this is a relatively modest increase and I also prefer the moderate plus implants to minimize rippling.

In my opinion, the best way to determine what bra size you will be after surgery is to place the actual sized implants in the bra. If the bra fits appropriately, then that is the size you will be. If the bra is too big, there will be extra space and wrinkles in it. If the bra is too small, the implant will bulge medially and perhaps push the bra away from your chest.
With thin tissues, it makes a great deal of sense not to use too large an implant as doing so would cause problems with time such as implant being felt, implant visibility, and sagging.
High profile implants work well, provided that the diameter fits your frame and is not larger than your breast base width.
Anatomic implants are teardrop shaped with more projection in the lower part of the breast. When you look at the breasts in all positions (standing, lying down, on your side), it is a no brain-er that round implants look more natural. While you are standing, the round implant takes on a somewhat teardrop shape. The big difference is that when you lie on your back, round implants looks round like a natural breast, but anatomic implants stay teardrop shaped which looks silly.
Sounds like you can achieve a really nice result.

Increasing the volume will probably keep the width similar but you have more projection with these implants.