Of the HW's listed, I would favor Overeem against Schaub only. To quote BJ talking about GSP, Overeem is a frontrunner, a bully, and when he gets pressured he's gonna quit.
He's quit before as has his brother and all the physique in the world won't help when he's fighting guys other than Duffee and Werdum. Cain, JDS, Brock, and Mir would all be able to take him down if they wanted and as soon as he starts getting hit he'll crumble. The guy's a fraud.
His win list includes Duffee, Rogers, and Werdum.
He's lost to Werdum, Sergei, Rua x2, Arona, Nog Lite x2, and Liddell. He's gonna have alot of upset fans if and when he comes to the UFC.