Strength and the amount of chakra aren't the only things that matter. The fact that Kabuto was smart enough to start healing himself before the rasengan hit him is proof that he is very smart. And being smart is key in battle. I think with what we've seen so far of kabuto is enough to tell that he is on or above the level of kakashi.

hm i just contridicted myself. I think i said the opposite thing is another post.