Ok, about Gai being able to avoid the Sharingan. Kakashi is Gai's rival. Gai probably spent A WHOLE TON OF TIME practicing being able to fight extremely well with his eye's closed. plus his area is taijustsu so he has an advantage. But I don't think Sarutobi spent much of his time practicing to fight with his eyes closed. And who knows if there is a Konoha technique that can defeat the all mighty MS.

And about the question if Itachi could even beat a Sannin:

Tsunade had trouble with Kabuto, so I don't think we're going to even consider her.

We've been over this millions of times that Orichimaru admitted that Itachi is stronger.

The situation is flaky on if Jiraiya>Itachi or Itachi<Jiraiya. Thats all for now, I'm tired of typing/