I don't even think that Kisame is as strong physically as people assume him to be. I think it's just Samehada weakening the opponant by taking their chakra. Alas, I don't doubt that Kisame has a huge chakra pool because he practically made a sea out of nowhere when he was fighting Gai.

I think Kisame is better than Suigetsu, if he's made of water, you'd think he could be controlled by a water type jutsu user, lol. Unless Suigetsu has some trick up his sleeve. Maybe Zabuza's sword is the counter to samehada.