How about Toquinho? Other than his brutal subs (and ******ism) all you hear about that guy is how freakishly strong he is
I would say randleman,but remembering now Rampage was stronger than him,so I guess its either Randleman or Rampage.
Overeem does look crazy strong at hw now, but he hasn't really proved it yet. Throwing around Brett Rogers is not really proving it beyond doubt. If he does that to Cain and Barnett, I'll start believing. Rampage's powerslam of the exceptionally strong Arona and his dominance of Randleman put him right up there. GSP's domination of strong wrestlers is amazing too, though he did have trouble keeping Thiago Alves down, Alves being a powerhouse himself. Mark Coleman was a monster in his prime, though it was all supplemented by juice I expect. GSP or Rampage.
Hmm... If it wasn't pound for pound, Sapp would do pretty well in this thread. He didn't have anything but size and strength.
Practical strength has to go to Hughes but he was a big guy at 170 so I'd say Rampage because 205 guys can often be heavies. No matter who it was, Rampage could and would lift and slam you.