I only heard people say he hits as hard as a heavyweight, not that he hits harder than most HW's. Therefore i believe most HW's would take his shots which is only natural due to the huge size difference. I also believe that some SMW's like Abraham, Kessler and Froch could have a chance of surviving. The higher the weightclass, the lesser damage he would do. Still a tremendous puncher though.
Prime Amir Khan I can already see it.. GGG hit Khan so hard he thinks Khan is going to go down but Khan just grin at him. GGG looking at Khan with intense pain and suddenly start screaming and crying holding his hand like he hits a metal wall .
Delayed reaction and then this happens to Khan's head http://img3.wikia.nocookie.net/__cb...rchive/b/b5/20120914120348!Exploding-head.gif
Far too many to count. GGG is a bum that has never faced an A level opponent. Abraham would beat the beets out of the Russian.
He didn't so much take it as run from it. Really you're looking at going up a division. Of the MWs, Murray has the best chance of taking GGG's punches.