Kisame beats the 3rd Raikage with no more than mid difficulty.
-The third Raikage speed shouldn't be an issue for Kisame, since he was reacting to Bee, and his samaheda was taking 6 tails worth of chakra off bee with one swing. Without the Raiton shrowd, THe raikage's nukite won't damage Kisame anywhere near as much. A few swings of Samaheda will leave the raikage drained.
-Water clones can be used as a distraction, to possibly catch the 3rd in the Water prison jutsu.
-The third raikage has immense durability, but once his chakra levels reaches zero, he should die.
-There's also the Water dome, and GSB. If Kisame uses the Water dome early and fuses, the 3rd Raikage gets shat on.