But susano'o activation was quick enough to halt Kirin....Pretty sure it could halt a rasengan
Feat for Itachi, not Sasuke. Its already fact that Itachi's reactions surpass Sasuke's.
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which wouldn't be possible if he wasn't able to react.
Not to mention when the user and the Susanoo have been separated.
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And a second one can't be used while the first one is still up, or Madara wouldn't have been forced to use Preta Path.
The Kyuubi's chakra doesn't make a difference as we have yet to see how it enhances Minato.
Sasuke should take this, mid to high diff.
It would actually give him protection from the Enton Flame that covers Susanoo as it doesn't burn fast (Only the one that covers Susanoo as seen against Ay) and the cloak has shown to be flame resistant many times, and they would give him chakra arms. Which can be useful as:
-He doesn't need to touch Susanoo with his own hands so coating it with Enton wouldn't stop him from teleporting it away.
-He doesn't have to get in short range of Sasuke's Susanoo.
There's also the fact that more chakra=more clones.