Re: What we need to know is what is stronger Kyuubi's or Nature Chakra?
So I mentioned this in another thread, but, I don't think the Kyuubi Chakra is necessarily going to enhance Sage Mode directly.
Sage Mode is already pretty powerful. Currently the biggest limitation to Sage mode is the ability to gather up enough Sage chakra to maintain it.
In the Manga, Pa tried to Fuse with Naruto in order to facilitate the continued accumulation of Sage chakra while in combat, but they were unable to fuse because the Kyuubi interferred with the fusion between Naruto and Fukasaku.
If Naruto can master the consciousness of the Kyuubi, or at least get it to work with him, he could have the Kyuubi gather Nature Energy while he fights using sage mode.
That alone would negate the current weakness to Sage mode.
On top of that... I'm kinda wondering if the Kyuubi has a natural affinity for an element or elements.
Every Bijuu we've seen thus far has at least one elemental affinity, but they've not really said if or what the Kyuubi's Elemental affinity is.
If I had to venture a guess I'd say Fire, since alot of imagery associated with the Kyuubi involves Fire. We already know that Fire pairs with Wind, enhancing the destructive ability of Fire Jutsus, but just because the imagery fits doesn't make it so.