Only advice I can give you so far is that
*Overs probably do look more fake, however that all depends on the person and their frame. 525S in one person could look a natural size.. whereas in another person they could look too big and fake. seeing as you have quite a bit of breast tissue already with being 34c, i *think* you would be less likely to gain the fake look as i believe the tissue will cover over the edges of the implant very well.
*Overs are said to give better cleavage. think this is cause they push together better.
*With unders you apparantly lose 10% of the size. but for 525s i wasnt given the option of under the muscle as traynor said they were too big for that.
*Sagging is not affected by over or under the muscle as this is what i asked in my consultation. The only thing that does vary from over or under is where the sagging occurs on your breast. The thing that obviously does affect sagging more is the larger the implant – the quicker you will sag – just the same as the way natural boobs sag really.
Can i ask your stats? cause you cant really say whether they will look natural or not because its all dependent on your body at the moment.
Hope iv helped! x