I don't think Naruto has the will to fully use the kyubi chakra to it's full power. He wants to incapasitate Sasuke not kill him. So I think that will hold him back from winning the fight. Plus we have no idea how powerful the Lv2 seal is or how it affects Sasukes Sharingan. Some new power could come from that combination that we don't know about so I'm still up in the air about who's gonna win.