Kamui Shurikens can be easily countered by throwing the Magatama in its path. Just like Kakashi did with the Chakra arms. They were coming straight at PS and he simply intercepted them. It has less to do with speed and more to do with precision. Like Sasuke's arrows were intercepted by Black rods. Those black rods obviously were not shot out at arrows' speed, but they were so in time, as the enton managed to eat the rod and disappeared.
Same will happen here. It isn't about speed, but interception.
Same will happen here. It isn't about speed, but interception.