And what's wrong with what I said? Naruto is more powerful than Sasuke. Naruto is just less skilled than Sasuke. That's where the difference comes in. If they are the same speed or even if Naruto is just a tiny bit faster Sasuke's going to be able to win because of skill and the sharingan reading Naruto's movements. But in the tailed-form reading movements won't help as it was shown in VotE, and the more tails he gets the faster he gets. He'd be able to blitz Sasuke using 4-tailed mode, and nothing Sasuke has shown could penetrate the chakra armor it creates. The only real problem is Sasuke now uses genjutsu which Naruto has no defense against.
Naruto using Kyuubi isn't slower at all, chakra armor isn't getting pierced by anything Sasuke has, and Sasuke won't be able to predict his movements as the fight at VotE proved. Where is the if? Naruto is much more powerful, and he can heal from anything Sasuke does also without even going 4-tailed. 3-tailed for would be just fine. The only way Naruto has no way to win is if he uses his own chakra and doesn't go into his tailed forms while forgetting all the skill he does have and just spamming shadow clones. Which because it's Sasuke he probably will do because Sasuke always has to win it apparently.
4 tails was being bested in the speed department against urochimaru. also. other then the extended arm chakra etc, 4 tails was said to be WEIGHED DOWN by the cursed chakra and unable to move, it wasnt exactly flying around either. and seeing as sasuke has his own{and possibly the most powerful } mangekyo now{even thougj saly he refuses to take itachi;s eyes which makes little sense to me} it shud more than make up for his cursed seal{even though i loved his cursed seal and am gonna miss it a lot} and he definately has surpassed itachi NOW. plus his mangekyo is the coolest.