Naruto required his strongest technique to bust Madara's Chibaku Tensei, and he referred to those as mere raindrops. That, along with the fact he made many of them, and is the Juubi's Jinchuuriki, heavily implies that he can make some, much much larger than what he did in the manga. Then we have Bijuu Dama, which Madara can infuse with Senjutsu, and once that is fired, Naruto dies. If you only take what Madara showed in the manga before his defeat, he loses, but if you take into account everything that he can do (as in proven stuff) then he'd beat Naruto.
Gai's individual (Not the whole 5 steps) Evening Elephant hits wouldn't break through PS, they wouldn't even do any damage, if they did, it'd be very little. Kakashi's PS is enhanced with Rikudo's Chakra, as is his other stats, like speed, strength and Ninjutsu. Gai isn't breaking it with Evening Elephant alone, and if he uses Night Gai, he dies while Kakashi phases right through it.
And no, Gai isn't fast enough to blitz Kakashi w/ Obito's power.
As for Juubito, Gai can't get past the Gudo Dama. Minato already stated that he can't touch it, and if Obito is able to get Bijuu Dama off, or a Gudo Dama explosion occurs near Gai, then he'd die. If Juubito releases the Shinju, it gives him more than enough time to do any of this.
1.Kaguya
2.Hagoromo
3.Madara
4.Naruto
5.Sasuke
6.Obito
7.Kakashi
8.Hashirama
9.Nagato
10.BM Minato
9 and 10 are debatable, but I believe that Nagato can win it with very high diff.
There wont be power-up for any character anymore, at this point of the manga they all reached their prime once, and now there must be a top 10 with the 10 strongest ones on their prime. So there wont be more than 1 version of each character.
This is mine:
1- Kaguya
2- Hagoromo
3- Rikudou Madara with both rinnengan
4- Rikudou Obito
5- RM Naruto/ Rinne Sasuke
6- Rinne Sasuke/ RM Naruto
7- DMS Kakashi
8- 8G Gai
9- SM Hashirama
10-BM Minato
Featless characters were excluded, like Hagoromo's brother, Ashura and Indra, Shisui etc..
My top final 10 would be
1- Kaguya/3 Rinnegan Madara
2- Hagoromo/Rikudou Madara(2 Rinnegan)
3- Rikudou Madara(2 Rinnegan)/Hangoromo
4- Juubito
5- RM Naruto/ Rinne Sasuke
6- Rinne Sasuke/ RM Naruto
7- DMS Kakashi
8- 8G Gai
9- SM Hashirama
10-BM Minato
I put 2 Madara forms I know but they both exist and 3 Rinnegan Madara has Kaguya's 3rd Eye but not as much chakra as her...(they both have IT and can take chakra from their victims so... chkra it's not a big factor...) Also, 7,8,9 could be debatable though...