I agree with luimac about the part of the sharingan.
Also old granny said it. Official it's known that if you fight a Doujutsu-User 1on1, you should run away if you're not at least also Doujutsu-User and equally strong. But for a 2on1 or a greater disadvantage it can be really hard for a Doujutsu-User, coz he just can attack 1 person directly and while he's at it he has an open defense.
For me Kakashi is also just a really high ranked S-Class Jounin but no more. He might surpass the 4th and maybe also the 3rd Hokage sometimes, but for now he is far away from the level of a Sannin.
Also Kabuto, who seems to be nearly equal to Kakashi, has a long way to go to reach Kakashi. He may have more Jutsus (and some are real mad!) but Kakashi learned to use the Sharingan really good while the timeskip and I dont see any development for Kabuto.
I wouldnt count on Kabuto in a fight between him and Kakashi.
There are just to many disadvantages on your side while fighting a Sharingan-User.