Silva is susceptible to TKO by someone mounting, then GnP. There's some solid GnP'ers at 205.
GSP has shown sometimes he can get rocked, even tho he looked great standing against Alves and can basically TD anyone who's giving him trouble.
Lesnar's been rocked before (said he saw stars after a knee from Mir) and he's facing heavyfisted guys, so he's most likely.
Penn fights in a division without KO power for the most part. Diego doesn't have any proven one-shot KO power and Penn has cleaned the rest of the division. If he fights at 170lbs, against for example Alves, he'll probably get TKO'd.
Lyoto is the man, end of story. By the time he had 5 MMA fights under his belt, he had beaten Rich Franklin AND BJ Penn (fighting at 191lbs). He never gets hit, and he has a strong chin - just ask Inoki. I don't think we will ever see Lyoto finished, let alone knocked out.