Kisame made a sea/ocean around a massive desert style rocks with only 30% of his chakra, and he didn't even seem tired from using that jutsu, and he used other arrays of ninjutsu after that as well, and STILL had buttloads of chakra left to use, its just gai used 7 gates to beat him.
Kisame has tonnes more chakra than even naruto, neji said he had more than naruto, and naruto has MASSIVE chakra, more than Jiraiya and enough to learn sage mode pretty fast.
Kisame is a very strong ninja, like ive been saying when kisame said against jiraiya "oh no not a sannin" i think he was being heavily sarcastic.
I don't think he's the most powerful in akatsuki (unless kishi decides to do what he did with itachi and give him loads more weapons and defences to make him overpowered) but he's still very powerful.
What everyones gotta realise is Kisame hasn't actually used any of his advanced techniques, and his aim against gai was to slow them down too.
I'm sure kisame has a few trump card ninjutsus which will be awesome