Bee solos low difficulty.
EDIT: I'll make it extremely logical for the logic wackboys out there.
1. The reason why Killerbee takes this is if you recall when he fought Sasuke (Who is actually much stronger than Guy and Kakashi put together got fodderized.) Basically Kakashi was fighting against a blind worn out Sasuke and started to stagger when Sasuke used the full susanoo. But back to Killerbee now, Kakashi charging with a lightning edge and in this scenario Bee could counter it by grappling onto Kakashi throwing him or just stab him with his swords.
2. Kakashi uses Kamui against Killerbee, now Killerbee can use number 8 to move fast in order to evade Kakashi's Kamui. Another thing is that Killerbee transforms into 8 tails Kakashi is basically a sitting duck because he is exerting a huge amount of chakra while 8 tails can just bijuu dama his ass skyhigh.
3. Guy Might is much stronger than Kakashi due to his 8 gates technique. Guy could probably counter Killerbee's taijutsu attacks until Killerbee stir Raiton into the mix causing Guy to avoid deflecting his attacks. Now for the sixth or 7th gate it could go down, but eventually Guy would wear out leaving Killerbee to finish the kill. The 8 gate would injure Gyuuki and Bee, but Guy would still end up dead.
4. Bee outsmart Minato. He isn't a stupid character.
Bee takes the trophy here. A lariat can do away with Kakashi in seconds.