Frank Mir says that Brock Lesnar could beat Fedor Emelianenko
“I think it’s an excuse to dodge top level competition. As long as he never proves he it, he can always keep the number one ranking. But if he goes into the cage and loses, he loses that. In a boxing ring, when you’re taken down, you can scoot from under the ropes, you can survive. In a cage, you better be able to get back up, or you’re gonna get crushed. He would get crushed against Brock."
I think that Fedor is a smart enough fighter, and well-rounded enough that he would be able to adjust to fighting in a cage, but I still think that Lesnar would have a great chance against him.
Contrary to popular belief, Brock Lesnar doesn't rely solely on his size, as guys like Tim Sylvia have done. Lesnar's wrestling is at a world-class level, and that's a huge part of the MMA game. He could take down Fedor, and once that happens, he could quite conceivably control him on the ground, and ground-and-pound his way to victory, as he did against Mir and Couture.
Fedor is still the best until he gets beaten, but it would be nice to see him actually try to prove it.