I think being a guy who walks around at about 170lbs, stepping in with Brock would make me poo my pants. The guy's fists are probably the size of my head.
Coming from a big boxing background i'd love to step in with Frankie Edgar and just box with him for 15mins and see first hand how good his movement and speed is.
Seeing as i am british and have therefore done about half an hour of wrestling in my whole life i'd hate to get in the cage with Koscheck. Would be totally humilliating being held down for 15mins and being able to do literally **** all about it.