They'd murder him. I could be wrong, but I've seen a lot of Overeem's fights and neither Brock nor Carwin would have much trouble taking Overeem to the ground. And Overeem and his backers talk about punching power but Carwin hits much harder. Overeem is overrated just like a lot of the Strikeforce crew. All the, eh, sudden muscle he's put on hasn't helped all that much either, lol. Overeem is a dirty fighter, as in dirty as hell, and that could add something in terms of Brock or Carwin really getting steamed in the middle of a fight. I remember Overeem's fight against Crocop where he kept intentionally kneeing Crocop in the groin. Overeem's chin might be a bit suspect too. I think he's been KO'd, as in out cold, 6 or 8 times, but I'd have to look that up.
He's the strikeforce heavyweight champ. He just fought Brett Rogers and Rogers just KO Arlovski not to long ago, but appears to have gone down hill so don't know if that's saying much. Just curious what others thought of him. I hear people hyping him up.
I don't think he could beat Brock or Carwin either.