Kamui is faster than bijuudamas? Ok, but have you forgotten that for Kakashi to warp something of that size he needs time to mold the correct amount of chakra? If there are five bijuudama coming at him he has to mold the chakra for each individual ball, which he cannot do in time. Please re-read the chapter where he attempted to warp the gedo mazo's head, as it clearly showed that he takes a while to warp large things. Also please re-read the chapter where it shows his conversation with Shikaku, where he clearly says he could not warp large things until he received the kyuubi's chakra.
Now, I know that you will simply counter with "I am talking about Kakashi with kyuubi chakra. kamui is the fastest is the whole world," but wait, theres more. With the kyuubi chakra Kakashi was only able to warp something large, in that case, gyuuki, twice before the chakra was used up. So maybe he can warp two bijuudama... but the other three are going to get him. Or, if you are still adamant, I welcome you to go to the vs threads, create a thread titled "Kyuubi cloaked Kakashi VS the entire shinobi world," and see how thrashed your favorite character gets.
I tried thinking of things using your logic, and the only conclusion that I have come to is that Kakashi's kamui would be one of the strongest techniques... if he was the kyuubi jinchuuriki. As that is most clearly not the case, may I say that we have come to terms, and put this thread to rest?