It would only be adult Naruto or adult Sasuke, not both at the same time. Could they defeat the entire Akatsuki by themselves? Akatsuki meaning Six Paths of Pain, Konan, Itachi, Kisame, Kakuzu, Hidan, Sasori, Deidara, and white/black Zetsu.
There are no limits. Itachi has his susanoo and his...