http://www.mangahere.com/manga/one_p...7/c562/10.html) you can see Vista is as relaxed as Mihawk is, even with Mihawk fighting with enough force to destroy the giant glaciers, shred Buggy into pieces, and absolutely thrash Luffy. So, since we've yet to see Mihawk, or for that matter Marco and co, fighting all out, we can't accurately judge. From what we've seen, though, the average Shikibukai is about even to a Yonkou's top crew members, but still leagues below a Yonkou. Mihawk is incredibly strong, but his fight is still to come. Still, I can't see any Shikibukai being able to stand up to Whitebeard. When old and ill (to the point Marco commented on it) and having just been stabbed, he still got Sengoku frantically screaming at his thousands of men, including all 3 admirals, the Shikibukai, plus incredible fighters like himself and Garp. Whitebeard stomps.
I'm not saying the fight wouldn't be interesting (a couple of comments ago I was bouncing around ideas as to how Kuma could hurt WB), but I'm saying that ultimately , Kuma is powerless to stop WB.
On an unrelated note, Uriel, the whole 'betting' idea is really fun, it's not often I do more than just play the devil's advocate for the fun of it
If it goes like that, then Kuma would've become PK long time ago, his ability is haxx, but not as haxx as people tend to believe IMO
Although, I like Kazu-Sama's idea about repelling his own fatigue and such, but there's no way that would heal his wounds or such a thing, let's say he got a cut in his cheek, no way it would heal if he repelled his fatigue in that moment. But such an ability is useful only for someone who feels pain, example : Luffy got injured and tired, Kuma comes, repels his fatigue, Luffy can now fight but still injured. Such a thing could be even called dangerous because that would put his body into much much more serious strain. But since Kuma isn't even a human, and doesn't feel pain to begin with, repelling his fatigue is useless.
Every ability is HAX up to a point when someone has a HAXXER ability in One Piece. Thing is that Gura Gura is powerful, but it's not handy. In the other hand, Paw Paw is not only powerful, it's only extremely versatile.
Nikyu Nikyu No Mi offers a nice set of powers (repel air, repel fatigue, teleportation, compressing air, repellling attacks), but I don't think it could ever compare to Gura Gura no Mi, there's a reason BB went through such a trouble to get the Gura Gura no Mi (a bit off topic, but I was wondering how the hell was he gonna get the Gura Gura no Mi originally ? Because he wanted to turn Luffy to the Marines to become Shichibukai, no way WB would make war with the Marines for Luffy, albeit Ace would've done it... It seems as if BB was really lucky to have faced Ace instead of Luffy, because I don't think he could've defeated an uninjured WB no matter what)