Should I get 350cc or 375cc?

There will be no visible difference between these two implants. They are almost identical in size. For instance, if you are using Mentor implants, both have 4.8 cm of projection. There is a 3 millimeter difference in base width, 11.7cm vs 12cm. I would highly doubt that you will be able to see 3mm of difference.

Keep in mind that the difference of 25 cc of breast implant volume may not even be noticeable clinically. 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'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 “C 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 may be 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. 

Thank you for your question. It is much better to accurately discuss implant volume and projection with an in office exam and detailed measurements. In order to make an accurate size recommendation, I would need to assess your chest wall and breast mound measurements/characteristics. I use these measurements to help me during the sizing process to guide you to a safe result for your chest wall and just as important, one that meets your end desires.The next step is to try on this range of implants in the office with your doctor. The key to this success is showing your surgeon the body proportion you desire with a bra sizer and allowing your surgeon to guide you to the right implant. It will be much easier to communicate in implant cc's than cup size when determining the appropriate implant for you during the sizing process. In addition, review of photos and use of rice bags can be very helpful to the patient and surgeon in achieving a safe and happy result. Close intereaction and involvement from your surgeon during this process can help alleviate the anxiety and fears of choosing the right size. I wish you a safe recovery and fantastic result.Dr. Gill