It all sepends on how much damage BB can take, if he can take a sword slash from shanks and give back the damage 2x then he'd have a really good chance.
But if shanks attacks are really powerful BB would be a fool to take them since they would severly injure him.
When it comes to devil fruit users BB has the edge but against the non-devil fruit big boys I think he would lose. He isn't ready yet ince he was trading blows with ace who isn't the strongest of characters.
Who said he'll actually use the ability against the person? He got Shanks without it, imagine what will happen if he used the ability around the surrounding plus his own combat ability. That can seriously own. Take into account he didn't really master the ability too.
And yeah, I know I'm late on the reply. Couldn't help but answering.
Anyways, cut the Shichibukai level crap. THEY DON'T HAVE ONE. It's a force that if gathered, equals the Yonkou, or gathered+Admirals, or anything like that that's maintaining the balance. You can see Mihawk for perfect example. He might beat Shanks' in a fair fight, but hey, he's a shitty Shichibukai.
Also, we don't know anything about WB or Doflamingo, so how can you say anything about a fight? Hell, we can't even point Ace's strength other then the 2nd division captain thing, and that's not enough.