In this case, just a Madara and Hashirama fight on a much larger scale. Hashirama stills win. Naruto still posses a large chakra reserve and Kyuubi's chakra, along with Sage Mode.
Well Naruto used them so what's the difference? Also it's not Sasuke's fault that he is strong enough to wield them for his benefit so why wouldn't he use them?
It's just a big idc. There are like 1-2 chapters of the fight left. Sasuke probably wouldn't have been able to beat Naruto if he decided to go all out so he just had some insurance and it was also a means to end Naruto as fast as he could.