Surgeon doesn't want to go larger than 345cc, but I want bigger - should I ask about doing saline implants instead of silicone?

Using the breast diameter to determine implant size is faulty in my opinion. It may seem precise but it's really not. I think a350 cc implant is a very common size to use but I'm sure you could go bigger. Saline or silicone are both fine. You should read up on the difference and the pros and cons of each to make a decision.

Please do not go larger than your surgeon recommends. He/she has examined and measured you and knows the best range of sizes for your tissue and frame. If you go larger, you will thin and stretch your tissue more and sag more. Also, going larger with saline may show ripples more and saline are more firm. If you have little breast tissue, you will have better results with gel implants.

One important reason that your surgeon has recommended that you don’t go beyond a certain size is that anything bigger will increase your risk of complications. These complications include wound separation, where the closed incisions reopen, and skin that gets too thinned out in an effort to cover the implants, which can also increase visible rippling. If you really want to go bigger, consider getting the implants in the recommended size now and then waiting to have another surgery at a later time, after tissue expansion occurs and your body is better able to handle larger implants.