Speaking of duration, have we ever seen Naruto actually run out of Sage Mode without it being because he uses it all up with Rasenshuriken? The only times I recall him running out had ended with him using Rasenshuriken and that one time he was drained by the Preta Path.

If we're taking personality into account, I'm not sure if Naruto would risk using the Rasenshuriken on Sasuke and accidentally killing him. Maybe if Sasuke was protected by the Susanoo, but in their last fight, Naruto couldn't bring himself to fire the Bijuu Bomb at Sasuke when he was in his Perfect Susanoo either. He did use that super Rasengan while in his Asura Kurama mode, but that might have been because he knew it would just cancel out Sasuke's attack midair.