Of those heavyweights, I think he would beat Couture, Hardonk, Werdum, and possibily Sylvia, maybe Gonzaga if Silva can get it past the first round; as for the rest, no. Just because he fought at 205 doesn't mean he can fight heavyweights. Good god, the size differential is enough to decide the fight.
To quote Mr. Irvin, "there's weight classes for a reason."
Using that logic, shouldn't Fedor have lost to Hong Man?
Shouldn't Cro Cop have been owned by Bob Sapp?
Shouldn't BJ Penn have been crushed...many times?
Also, don't forget, A. Silva is 6"2.
Even then, skill > size any day. Just because he can't toss Lesnar around like a rag doll doesn't mean he will let Brock get a hold of him. And being heavier doesn't make you less likely to be knocked out.