The big advantage of Naruto with Kyuubi chakra is he can become, like, 9 S-class fighters. And even individually, Sage has a bit of an advantage in pure taijutsu, but Kyuubi Chakra mode is more versatile, has higher speed, has all those arms, etc..
Sage Naruto could beat Feral 4-tails Naruto, but once Naruto has full access to the chakra, he beats his Sage form solidly.
Depends on which Sage Mode Naruto and which Kyuubi Naruto.
I'd reckon the Sage Mode Naruto that fought Pain would beat 4-Tailed Naruto and the lower versions, but would lose out to 6 Tailed Naruto, though the Frog Song could net him the win. This SM Naruto would lose to Kyuubi Chakra Mode Naruto as well, and the Toad Elders might not have a chance to use Frog Song as KCM Naruto knows about its weakness.
The SM Naruto that fought Kurama in the mind-scape battle (i.e. the one where he had no trouble making hundreds of Shadow Clones, each with Ultra Big Ball Rasengans) would give KCM Naruto problems, though the latter's creativity with Chakra arms could still win it for him. We also don't know if Naruto can currently make that many clones in Sage Mode.
If it is the Kyuubi Naruto that can enter Tailed Beast Mode, then he wins with very little difficulty as his raw power output and speed are too great for SM Naruto to overcome.
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