Do moderate profile implants appear larger than high profile, and if so, what would 350cc high profile implants be in moderate?

Overall, the moderate high implants, the lower height, will give a more natural look than high profile implants. The high profile may give a little more upper fullness or ball look. However, women who have narrow chests and want fairly large implants, the high profile fits better. Please discuss your concerns with your surgeon who has examined and measured you.

There are no absolute rules when it comes to selecting the appropriate breast implant for a specific patient.  In many ways, breast augmentation surgery (similar to other plastic surgical procedures) is as much an art, as it is a science.
 Keys to success:
1. Careful selection of plastic surgeon.
2. Careful communication of your goals (in my practice I prefer the use of goal pictures, direct examination/communication in front of a full-length mirror, in bra sizers, and computer imaging).
3. Careful measurements (dimensional planning) will be critical.
4. Skillful execution of the procedure,  involving many critical steps, including careful dissection of breast implant pocket.
 Generally speaking, the best online advice I can give to ladies who are considering breast augmentation 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 are looking for. Ask to see lots of examples of his/her the morning yes thank you 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. For example, I have found that the use of words such as “natural” or "C or D cup" or "too large" 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. Again, the use of computer imaging has been very helpful during the communication process, in our practice.
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, after the use of temporary intraoperative sizers.
I hope this helps. Best wishes for an outcome that you will be very pleased with.

Most of my patients select HP or moderate+ Mentor implants. The difference is in the projection from the breast wall. Slender women generally prefer the HP. Did you try on a profile bra with silicone moderate 300cc and 350cc sizers under a tailored blouse, tight sweater, swimsuit, workout clothes, tank tops, and other garments you typically wear so that you have the best idea of whether the garments fit as desired with the implant selected. I would recommend that you go with the size that boosts your self-esteem, and fits your anatomy.  Choosing an implant based on an aesthetic goal that exceeds your anatomic capacity may lead to complications and possibly revision.