I've done lots of studying into gigantism. Whether it's from acromegaly or simply a quirk of genetics, humans often suffer once they reach past a certain height. There's plenty of variables of course: People with acromegalic gigantism are afflicted with numerous medical problems, and no two cases are the exact same. Even for those naturally born to grow giant, the square-cubed law is a merciless bastard that makes the current design for the human body ill-suited for being anything taller than 7 feet tall, let alone 8...
...but what about an older design? More specifically, the design of the stockier, more robust neanderthal species? They seem to tick a LOT of boxes for being better suited for gigantism than humans: They have a squatter, more robust build (better suited for heavy bodies), they have straighter spines (which may provide better support in standing) and their bones were naturally heavier and stronger than us modern humans (bone structure is among the biggest issues with giant humans).
I'm writing a character whose design is derived directly from a neanderthal build. However, the character I made is 8'3 and calculated to be nearly 700 pounds. Would a neanderthal body structure alone be able to compensate for this kind of size and weight? Or would it be necessary to make the bones more dense, like an LRP4 gene mutation? The character in question is a product of genetic engineering, and thus does NOT need to be refined for any kind of survival in the wild. It's just another story of unethical humans playing god.
Question is, would a story with this premise be realistic? Can a giant with a neanderthal's skeletal structure handle it's estimated size and weight?