I don't think a curse seal will be enough to give Sasuke the edge over Naruto. The only power up Sasuke could get at this point is probably rinnegan.
Lots of foreshadowing has occured through out Naruto, primarily the connection between Naruto/Sasuke and the Older/Youner son of the Sage of Six Paths. If I had to guess, Sasuke and Naruto's final battle will be the deciding fight between the two decedents, since Naruto is an Uzumaki who are relative to the Senju and Sasuke an Uchiha.
It will be the fight that determines peace between the rivaling clans and the world. It only makes sense that Sasuke receive the rinnegan then, because he is the last remaining descendant of the Uchiha and the Older son, who also had the rinnegan.