Naruto would still annhilate Sasuke. Don't forget that Sasuke is much weaker than he was since he no longer has Orochimaru's power. Also, Jiraiya did okay against Pain even though he knew nothing about him. Now that everyone knows about Pain and that there are like seven of him he will be easier to beat. And because Jiraiya wasn't too bad against him (he managed to kill one of the Pains) and Jiraiya said he had trouble against 4 Tailed Naruto then If Naruto had like 6 tails he would probably kick Pains ass but there would be no one to stop him. And after his training on the mountain he will definitely kick ass. Also, he's not as dumb as everyone is making him out to be. After his multi-shadow clone training with Kakashi he got a lot smarter.
But Lee could still kick everyone's ass because I like him the best.