600cc vs 800cc? Would going bigger help to close the gap between my breasts? (Photos)

I have 600cc Mentor memory gel high profile implants. One breast is bigger than the other. I am wanting the implant in the smaller one switched out to make the breast match the larger one. Since I’ll be having surgery anyway, I’m tempted to just get larger in both and go to 800cc. I am 5’9, 125 pounds. I have wide set breast unfortunately and my sternum sticks out so it makes my chest look skeletal. Would a wider implant help close the gap in between my breasts? I have had a 125 weight loss, and I’m wanting the internal mesh bra put in also. Would it be worth it to get the 800s? I see women smaller than me with 700-800s and they don’t look ridiculous. People are telling me to not go larger, but if the small women can do it, why wouldn’t I be able to pull it off? Also, when I lay on my back, they kind of go off to the side a little bit. What would fix this? I want them to stay up and be perky.