If I'm 34b, what will a 350g give me?

Thank  you for your question.There is no exact answer to this question as it will depend on your chest circumference and body habitus as also the kind of bras you will be buying. For the average body built this appears to be 2 cup sizes increase. I would advise talking to your plastic surgeon who can examine you and also give you sizes to determine the size of Implants that you need to get the desired results.Good Luck !!!!!!!!!!!!!!!

Thank you for the question. There is no accurate/reliable correlation between size of breast implant and cup size achieved with breast augmentation.
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 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) helps.