we have not seen Kurama use his full power by himself enough to now his real power. Naruto only has half of his chakara. And when he destroyed leaf village he was controled by Madara, So anything we have seen Kurama do doesn't really countas being just the nine tailed fox. If Kurama was full strength and not used by a Jinchuriki he could have some awesome power not yet seen so to guess at his powers is crazy. So it is impossible to know what his FULL power really is to judge against. But as for what we do know about them both Nagato wins mid-diff. with deva path.