Chuck didnt do well in any of his Pride bouts, its always been my theory that he's better suited to the octagon as opposed to a ring. UFC's rules help make him the best in the world, he uses them to his advantage. Now Rampage did beat him down, i dont know why but fact is he did it.
But from current evidence if they were to fight today, it wouldnt even be a close fight. The fight game is so different, on one hand you have Babalu going the distance with Fedor, but twice he is KO'd by Chuck. You have Rampage disposing of Chuck yet arguably he was beaten by Matt Linland. Youve got Amar Suloev going the distance with Chuck then being KO'd by Phil Baroni!!! You just never know whats going to happen. My money however would be on a Chuck KO