Well, Sasuke won the battle with Amaterasu, which Itachi possesses. I don´t see Bee winning for these reasons:
- Itachi was succesfully blocking Bee´s sword attacks, a feat that Sasuke wasn´t able to achieve: (Page 549/14)
- As I written before, both of them have Amaterasu that defeated Bee in original fight.
- Sasuke didn´t have Susano´o in this fight, while Itachi would have (along with Yata mirror and Sword of Totsuka).
- His intelligence and battle wisdom is greater than Sasuke´s, albeit even he defeated Bee (and yes, I know that Bee wanted to escape).
Itachi is similar to Sasuke, however with better Mangekyou, Susano´o, more battle experience, higher intelligence and better defence. As I wrote, I don´t see Bee winning this one. But I think genjustu would be anything important in this fight, because Bee is a perfect host. If I´m wrong, feel free to discuss with me.
And oh, this is my first post. I hereby welcome myself to Narutobase, yay
P.S.: (I´m not sure if my Avatar is allowed, if not, please, someone be so kind and send me a pm, thanks)