The 7th Gate could possibly the 5 Kages because he has Morning Peacock, Hirudora, EE but 8 Gate would just stomp all of the Kages. They would have been in a worser scenario than what Edo Madara did to them. Yes 8 Gates Gai could wreck Current Naruto and Sasuke at the cost of his own life since he wouldn't have anyone by his side to bring him back. :yeah:
Well I was with you until you said seventh gate can use evening elephant, that's a gate of death exclusive. And I'm terms of him beating current Naruto and sasuke unrestricted is debatable. Madara pre Shinju absorbed with one rinnegan was able to keep up with gai's movements, and his rinnegan doesn't have the sharnningan's precog, if preshinju madara could then sasuke also could, though sasuke can only with amenotejikara but that evades night gai, evening elephant is only being invaded if he can use a full force shinra tensei, ameno, or have some extremely durable asura armor.
Naruto has a chance also, but not through sheer speed alone, RSM Naruto will take gai's hits but still be damaged. But I think with his high sensing and agility in combination he can evade night gai, but seikzou (evening elephant) is a tricky one. Sasuke has the ability to evade gai's hits, and Naruto has the body. Though in direct confrontation, hits from evening elephant would decimate sasuke, and Naruto can't tank forever.