butt implants 430cc round semi solid & 605cc silicone breast implants with full lift

I had my surgery done by one of the only doctors I could find in Washington that does butt implants. At the time I couldn't travel to have it done. I had butt implants, breast implants with lift, and lipo of the flanks done. The butt implants are 435cc, the breast 605cc. I'm now looking to have them both revised.
The butt implants were done in the subfacia. When I'm just standing they look good, but any other position and they are very noticeable. If I bend over you can see the entire outline of the implant sticking out. They are also very hard. They have softened, but there is no way I could get away with saying it's natural. I would like to have my butt implants redone by Dr meja with larger cohesive gel implants. My goal would be 500cc.
I'm concerned that the extra weight of the cohesive gel will make my butt sag. Also, I'm worried that a larger implant wouldn't fit inside my muscle and I would end up getting a smaller implant then I already have. Does anyone have any long term updates with the cohesive gel and sagging? Are there and stretches/excercises I could do that would possibly allow my muscle to fit a larger implant?

I finally contacted Juan Diego Mejia about the proceedures I would like done. I want my current semi solid 435cc round butt implants removed and replaced with larger (as large as possible) cohesive gel implants placed intramuscularly. I want my breasts revised too, they need a lot of work. Not only do I ultimately want a larger implant, I will also need another lift. To make matters worse I believe I have capsular constriction in my left breast. It never dropped the way the other one did. I can clearly feel the implant when it moves around and there is some sort of "popping".... Add some full body lipo on top of that and ring me up ????.
I was quoted $7400 USD for the lipo and breasts plus $75 for medicine, $20 for labs $200 for massages. He told me I would have to wait for my butt because that's too much surgery. I wrote back asking if I could do lipo and my butt first and come back for the breasts.
That seems like a better plan anyway since it's difficult to communicate back and forth (email). It would allow more time to explain what's going on with my breasts and maybe do any touch ups I would need from the first surgery.
He (or whoever is sending the emails) said I would need to stay in Medellin for 15 days. I assume that's not including the two additional days I need to be there before the surgery. He said as a safety precaution patients need to wait 48 hours after their flight for their proceedures. I actually don't mind that at all. I was planning on coming a bit early anyway to give myself time to learn the layout of where Im staying and get myself set up.
As I was writting this I got an email back quoting $8700 for the buttock implants and lipo. I'm going to assume that's a ball park since there was no discussion about the size and availability of the implants.

After getting a quote from Dr Mejia I asked about available surgery dates. He responded "what month are you looking at?" That made me a little nervous because it's not what I expected. When I scheduled my first surgery they ran all the openings they had by me and asked what I thought. I told him after may I'm ready and asked when the earliest date he had was. He responded "after the first week of June I'm available. Look into what dates work for you and let me know." Now I'm questioning things because the situation just seems odd.