From the photos, you appear to have a fairly narrow breast/chest base and limited soft-tissue coverage in some areas, so 650 cc would likely be a large implant for your frame. That does not automatically mean it is impossible, but it does mean the decision should be based on measurements rather than a desired cc number alone. The “biggest” implant you can safely get depends on your breast base width, skin stretch, tissue thickness, nipple position, implant pocket, whether your current implants are over or under the muscle, and whether you have any bottoming out, lateral displacement, or rippling. If you already have 520 cc implants, moving to 650 cc is an increase of about 130 cc, which can be noticeable but may also increase risks. The risks of choosing an implant that is too large include thinning of the tissues, visible implant edges, rippling, bottoming out, widening of the pocket, more heaviness, discomfort, and a less natural shape. I would recommend an in-person consultation with a board-certified plastic surgeon, using your current implant information and precise breast measurements. The safest “max” is the largest implant that still fits your tissues and pocket without creating long-term distortion.