Is 600cc saline HP unders too large? (photo)

Thank you for your question.  It is best to return to your PS for further sizing and discussion.  The best results are always with implants that fit your frame and the base width of your natural breast.  We cannot comment on your specific sizing without proper measurements and a clinical exam.  I would share your concerns about rippling with saline and discuss the gel option with your PS.  For most patients, 600 cc is quite large for a first implant and the volume puts a lot of tension on the supporting structures with increased risk of bottoming out or the implants sliding to the side when you lay on your back.  Sometimes it is better to start with a smaller implant and then move up to the larger one after a year or two.  
The photos you send show results with a bit of bottoming out.  If they are longterm results, then this might be stable and acceptable.  If early post-op then it might get worse over time.
Surgeons are often relieved when patients pick a smaller implant because the results are more stable and the risk of positional issues is much less.  Your surgeon may have "recommended" a 600 HP based on your wishes at the initial consult but they will be much less stressed over giving you a great result if you go smaller.  I suggest all my patients come in for a second sizing (no charge) with a range of clothing (work, play, gym, bathing suit) and find that 80% of them tweak their implant selection.  It is good to have some time to consider your initial choices, sleep on it, and then revisit our offices a second time for more discussion and sizing.

Thank you for the question and pictures.  Based on your photographs, I think that you are starting at a good place and should have a very nice outcome with breast augmentation surgery.  
My best advice: more communication.
It is definitely worth spending more time (prior to the date of surgery) with your plastic surgeon to discuss further.  As you know, it will be important for many reasons, that you feel comfortable that you and your plastic surgeon are on the "same page" prior to proceeding.  Show your plastic surgeon what your goals using as many visual aids as possible.  This additional communication will go a  long way when it comes to helping alleviate your anxiety prior to proceeding.In my practice, the type (saline versus silicone gel) of breast implant utilized is individualized mainly depending on the patient's starting anatomy and goals.  The type of implant used may determine the final outcome, especially if the patient does not have significant covering breast or adipose tissue. For example, most surgeons feel that silicone implants have a more natural look and feel than saline implants because silicone gel has a texture that is similar to breast tissue. In other words, if a patient has very low body fat and/or very little breast tissue, the silicone gel implants may provide a more "natural" result (look and feel).   The use of saline breast implants may be advantageous for patients seeking a rounder, more augmented look.   Ultimately, you will need to carefully consider the pros/cons associated with each type of breast implant as you make your decisions.
 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 work. Sometimes, it is necessary to seek several consultations before you feel comfortable about your choice.
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 "D or DD cup” etc may mean 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, best not to discuss your goals and/or judge the outcome of the procedure performed based on achieving a specific cup size. The use of computer imaging may be very helpful during the communication process. The use of in bra sizers may also be helpful. In other words, use as many “visual aids” as possible during the communication process. I encourage patients to meet with me as my times as necessary, to feel comfortable that we are both on the “same page”.
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 generally select appropriate breast implant size/profile after the use of temporary intraoperative sizers and viewing the patient's chest in the upright and supine positions.
 
I hope this helps. Best wishes for an outcome that you will be very pleased with.

Patients often think in terms of cup size when considering augmentation. Unfortunately, devices are sized in terms of milliliters (cc) of volume. This can lead to some confusion when sizing. Additionally, it is important to remember that cup size itself is not standardized with variations from one manufacturer to another. Unfortunately, as many women can attest their cup size in an industry leader such as VS is not necessarily transferable to another brand.
Another point which is often under appreciated is that of anatomy and starting point. Any implant will add volume to the volume which is already present. The implant is additive. A particular volume will not necessarily confer the same cup size to different patients (often times it will not even confer the same cup size to different breasts in the same individual...remember they are "sisters" not "twins"). 
A general rule of thumb is that 125cc can represent somewhere between 1/2 to a full cup size increase. Smaller volume differentials (25-50cc) are typically less consequential representing a volume change of less than a shot glass. However, I have found these numbers, at least anecdotally, to be of little help. Patients often present with notions/goals which do not correlate with these sorts of sterile volumetric assessments.
When sizing patients, there are a number of useful tools including:
-3D imaging (has the added benefit of offering a volumetric analysis of the pre-operative breast)
-Breast sizers (rice bags)
-Goal photos
I also recommend that patients commit to a particular look rather than a cup size. Once a patient settles on a look that pleases them the overall cup size increase becomes less relevant.The key to obtaining a natural result is to stay within the parameters defined by your BWD. 
That being said, 600 cc is a significant implant. The larger the implant the greater the risk of complications and the faster the result will age as soft tissue attenuates/weakens under the stress/weight. You are smaller framed with little native breast tissue. With this in mind conservative sizing is preferred if you are seeking a "natural" looking result. Smaller girls rarely have 600 cc breasts. Silicone is typically preferred in patient with little native tissue to camouflage the device. Salines ripple more often than silicone and this will be more easily appreciated in a thin individual. Rupture rates are similar. Bottoming out is a function of technique and implant size (larger implants fall).
As always, discuss your concerns with a board certified plastic surgeon (ABPS).