To be honest I would prefer Swift Swim, but that would mean you need a weather setter and weather isn't really strong in singles. I doubles it's a different story though.
But based from experience, I don't think a CritDra is supposed to outspeed much. It's not a sweeper or revenge killer, but rather a wall breaker. It's main function is to break down slow walls that set up their defenses. If you want to run a sweeper set on Kingdra I would say run Choice Scarf/Dragon Dance instead.