If Sasuke gets the Rinnegan then he will be superior to Nagato since Nagato only has the Rinnegan and Sasuke has both the Eien no Mangekyō Sharingan and the Rinnegan.
I do think he would need a Perfect Susanoo or Perhaps a new technique the Eien no Mangekyō Sharingan grants him in order to beat Nagato.