Would 450cc HP implants be too big?

There's really no reason to leave anything to chance. There are excellent sizing systems to determine whether or not 450 cc breast implants look good to you. Determination of profile will be done by the plastic surgeon based on the anatomy of your chest.

The choosing of implants is best done in-person with a board-certified plastic surgeon.  A lot of factors can affect this choice like your desired end result, body measurements, breast tissue, and the like.  Best to visit a board certified plastic surgeon and get a full evaluation.  Best of luck, Dr. Michael Omidi.