@ohgodwhy: True, 8 gates Gai was waaaay too strong. It's ridiculous to think that Gai could have accessed juubi level power whenever he wanted, especially with how many times it would have ended everything. Gates are waaay too strong.
As for this fight? Gai should have this in the bag. If Madara was able to smack the 9 bijuu around with one rinbo: hengoku then I could see Gai hits in 8 gates at least crippling them.
R1: one at a time? Gai easily. I doubt he'd even need night moth. Anyone who doubts this needs to go back and read the manga, his striking power is mad. His weakest hit (the first hit of evening elephant) was enough to form a crater and push Madara several hundred feet into the ground- the same Madara who was barely pushed back by daytime tiger.
The strongest hit of evening elephant (the fifth strike) was able to smash through Madara's black chakra shield, which would have been at least as strong as the one Juubito was going to protect himself with against 4 juubidamas (I know the front was kamuid away, but Madara was smashed straight through the back). Bottom line: a complete set of night elephant hits should be enough to at the very least cripple any of the bijuu, even Kurama. Night Gai = insta death for them.
Gai wins 10/10
R2: again, Gai should take it- 30 minutes is plenty. For anyone who says 'but bijuudamazzz', how are they going to get a chance to charge any kind of attack, much less aim it, when they are getting blitzed by evening elephants? Gai could actually follow out a nice pattern with it (land a hit on the Ichibi with the first, send the second punch at the two-tails, etc). A small target that is strong enough to severely damage them and is much, much faster than they are is going to cause problems for them. I wouldn't be surprised if Gai sent their bijuudamas back at them either, if they did get the chance, using the force of his punch.
The best option for them would to be to aim at the ground in front of them and hope to catch him in the explosion- they'd get damaged, but at least they'd wipe him out if they catch him in it. But for that to happen, Gai would have to let his guard down or ignore at least one of them for long enough for them to charge a blast.
Going by the images I think 8 gates Gai can take out 9 chained up bijuu one on one and all at once, I mean they can't really move. On a serious note 8 Gates Gai should be the strongest Shinobi in Naruto right after current Naruto, Sasuke and Madara. 8 Gates is easily the 4th strongest current shinobi.
Hmm, I'm really not sure how Gai would stack up against current Naruto and Sasuke, but I think an argument can be made to at least put Gai on their level.