339/371cc to 450cc... Will this help me achieve the look I really want?

I might consider even larger as in the 550 to 600 cc range in my over the internet opinion.. Best to discuss with your surgeon again..

Thank you for the question and picture. Despite your good description of your body type and goals, online consultants will not be of specific enough help to you. Generally speaking, the best online advice I can give to ladies who are considering  breast augmentation revisionary 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're 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. I have found that the use of words such as  “natural”  or “more fullness/projection” 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.
 The use of computer imaging technology may also be very helpful during this communication process.

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.
I hope this (and the attached link) help.

Thanks for your question. I am not sure that such a small increase in implant size will increase your satisfaction. Best to discus in person.