How natural will implants look/feel on me? (Photo)

You can do over if, as a rule of thumb, you have at least 2 centimeters, almost an inch, of pinch thickness in the upper breast over the pectoralis. Less than this and you get problems like unnatural exaggerated roundness, shell visibility and palpability. Some plastic surgeons try to get an additional layer by lifting up the pectoralis fascia and making the implant pocket "sub-fascial". The nice thing about over the muscle is that you don't get any movement of the implant when you activate your pectoralis muscle. When implants are under (partially subpectoral, not fully) the appearance may change, with flattening or movement of the breast, not usually a problem, but would be nice not to have any motion.
If you have a lot of breast tissue you don't need such a large implant to get the enhancement in the wish pic, and that makes it even more likely you will look and feel natural.

Your photos suggest you have generous breast tissue that should provide good coverage with implants above the muscle. There are benefits to going under the muscle and these should be discussed with your surgeon before making a decision on implant placement.

You have plenty of breast tissue to hide implants nicely. When someone feels your breasts, he/she will be feeling breast tissue. Please do not go too large or you will sag over time.