Royal men and women typically had shaved heads and wore wigs instead. This is thought to have improved hygiene and comfort, but it would also have allowed more radical appearance changes between regions, not only within Egypt but also between Egypt and Mesopotamia. The beard we see on Sargon would not have been a real one but worn like a wig. It would be interesting to put a Mesopotamian style beard and headress on Pepi and then compare with Sargon.
It is very difficult to compare statuary. Techniques and forms varies from place to place. A king could be portrayed very differently as a old/mature man than he was as a youth. The statue of Pepi seems to have been from his early reign. The one of Sargon is perhaps that of a seasoned king.
Representations of the king also were idealized to increase their appeal to locals or to make them look more like a particular god, for example, compare the statues of Tutankhamun that made him look like the god Amun. So it is very doubtful that we can use this type of information to confirm or deny a potential association. Still, it's worth tyring.
I would also like to see a comparison of different types of Egyptian statuary. For instance, we could compare busts of Horembeb with those of Osorkon II (the "Libyan identity of Horemheb).
© Charles N. Pope, US Library of Congress. All rights reserved.