Sage mode heals you faster, seen when naruto falls from a cliff and survives, also he says "maybe now i can do it" when fukusaku stated that sage mode has amazing healing and regenerative properties.
Also, it doesnt matter anyway because narutos fuuton rasenshuriken is an INCOMPLETE attack, it always was meant to be thrown like a shuriken, hence rasenshuriken, not just fuuton rasengan
Fuuton is wind, rasengan is rasengan, shuriken means its to be thrown like a shuriken
which he has mastered as seen by the images when he throws one in sage mode and cuts through a load of stuff.
Since Naruto gave the name to the technique while he couldn't throw it yet, I think the name Rasenshuriken, is purely because it looks like a shuriken.
Maybe it's a hint from Kishi that Naruto will be able to throw it, but Naruto shouldn't know that.
And those cuts I don't think they they were from a thrown RS...
The way he cut those rocks couldn't be with a thrown RS, it has to be like his wind chakra, which is a razor-sharp, cutting element.
That part when we see those rock all cut in half, its probably him training his wind element, like when he was cutting the waterfall.
But know, I believe that with Sage Mode, and all his training he has mastered he actually threw waves of wind to cut those rocks. And will maybe use that against pain.
I'm beginning to think that it isn't a thrown FRS, cause when he did it on Kakuzu, it was like an explosion surrounding Kakuzu, and giving him countless attacks, and not a single clean-cut like in those rocks in Myobokuzan.
At least that's what I believe.