AND. In the next chapter tobi will say something about kakashi's unfulfilled promises and stuff. If tobi were izuna, how could he possibly know about kakashi's promises to an old friend? Only a person who knows kakashi well can know those things. And if he were izuna and he could know these informations about kakashi, why would he bother collecting them? what does he care about kakashi, his promises and habits?
In my opinion, Tobi knows kakashi pretty well.