I think the Danzou fight showed us Sasuke can be beaten.
Danzou could'nt use his full powers, his opponent had the most powerfull ninja ever on his side ( madara ) so he needed to conserve his strenght just in case, and Sasuke also had Karin on his side who basically told Sasuke all about Danzou's powers and even healed Sasuke.
I think this alone proved that Danzou could've beat him, and I am very sure Kisame could also defeat Sasuke without too much effort.
Not just Kisame, even Killerbee could defeat him.
Sasuke is very beatable ( in terms of logic, but knowing Kishi has the hots for him Sasuke probably won't lose any fight to come, just like the last 1000 fights he had ).
Now Madara on the other hand I can't say much about, it is known that he's the most powerfull, but we've seen little proof of that.