Um, right. Remember a while back Oda said that One Piece is only half way through, Zoro will be much stronger by the end of the series than he is now, same with all the other Straw Hat Pirates. So yes, i think that Zoro will defeat Mihawk.
And Doflamingo is...
WARNING MAJOR MAJOR SPOILERS!! WAY AHEAD OF K-F RELEASES.
Just incase you dont wanna read it, a quick run down is hes on of the Shichibukai.
Hope i helped.