What is the biggest difference between XL saline breast implants and XL silicone breast implant?

Dear Littlemishka,The two main types of implants are silicone and saline. The shell of the implants can be either textured (which reduces capsular contracture) or smooth. A textured implant sometimes requires a larger incision. The shape of the implant can be either round or tear drop shaped (gummy bear). Both have their advantages and disadvantages.
The different types of implant offer different pros and cons. For instance, the pros of silicone implants are that they look and feel more natural and ripple less.
On the other hand, the pros of saline implants are that they do not require as large of an incision as silicone, less expensive, they have less incidence of capsular contracture (scarring around the implant), one can tell immediately if there is a rupture, the size can be slightly adjusted, and they can be used for women less than 22 years of age.Daniel Barrett, MD
Certified, American Board of Plastic Surgery
Member, American Society of Plastic Surgery
Member, American Society of Aesthetic Plastic Surgery

Whether or not to use saline versus silicone gel breast implants for this type of revisionary breast surgery will depend mainly on the patient's goals. Most patients (who currently have 700 cc saline breast implants in place) who wish to achieve a "very fake" look choose overfilled saline filled implants.   These implants are more likely to achieve the more projecting round look compared to silicone gel breast implants. Saline breast implants tend to feel more firm compared to silicone gel breast implants. Of course, every patient undergoing breast augmentation surgery should understand that their anatomic starting point will limit the outcome of breast augmentation surgery.    In other words, a patient's starting anatomy will limit how large of a breast implant can be utilized safely. The use of a larger breast implant (than what is safely "allowed" by the patient's anatomy) can be problematic;  potential problems include breast implant displacement/malpostion issues ( such as bottoming out, lateral displacement, symmastia...)  and/or significant breast implant rippling/palpability.
 Semantics can be confusing; for example, the "internal bra" terminology has been used differently by different surgeons.  In our practice, the "internal bra" refers to maneuvers utilized ( generally during revisionary breast augmentation surgery) to better support the breast implants in appropriate position.  These maneuvers may include adjustment of the breast capsules (capsulorraphy) and/or the use of acellular matrix or  biosynthetic mesh.  The "internal bra" can be especially helpful when patients are experiencing breast implant displacement problems (such as bottoming out or lateral displacement).My best advice: select your plastic surgeon carefully. Make sure that he/she has significant experience achieving the types of outcomes you will be pleased with. Then, communicate your goals carefully, as discussed above.  Be careful about utilizing cup size references when it comes to communication.  In my practice, the use of computer imaging and goal photographs is much more helpful. Working together you will come up with a good plan to achieve your goals.  
Best wishes

The thing that both XL saline and XL silicone have in common is that they are both TOO BIG for you.  You are suffering from what we plastic surgeon call "breast greed".  A thoughtful plastic surgeon will walk you back from the cliff and tell you to thank your lucky stars that you have done okay with your currently VERY LARGE implants.