Re: Itachi vs Bee!
Sorry if someone said this, I did a search on "Kisame"
Madara sent Kisame to get the 8-tails if I remember correctly, don't have time to check the manga again. I think it's fairly clear (assumption, yeah I know) that Itachi was likely stronger than Kisame. No, there is a caveat. Kisame is a water element user, which is a weak spot for the 8-tails. Thus, I don't know how much that makes Kisame a better fit than Itachi.
We've seen how powerful Itachi is when he is sick and his sight has degraded as well as holding back on Sasuke. Thus I have no reason to believe he's going to lose except for stamina.
The 8-tails wouldn't be a pushover. Tsukiyomi doesn't work, and Ameratsu may not work if the 8-tails sacrifices a tentacle again. This exhausts Itachi's chakra, possibly giving some edge to the 8-tails.