Due to styles, Pac beats Castillo far more convincingly than Floyd did. Pac beats the shit outta Castillo. The difference in speed is too enormous for Castillo to deal with.
If we're talking about the younger Pac, who had more fighting desire and more killer instinct, then I think he stops Castillo late. Castillo didn't have an all time great chin, and to be quite honest, he'd have no defense for Pac's arsenal. Castillo is made in Heaven for Pac.
I think he has enough instincts and smarts to survive, to be honest... The speed would bother him enough that he'd cover up trying to counter with one big shot
Come on it's Manny Pacquiao..... Castillo will have to come down to 132...not gain more than 10 pounds before fight night....use 12oz gloves(while pac get to keep his 8oz)...Castillo will have to take olympic style drug testing that huge face and chin ain't kidding nobody(pac doesn't have to drug test...he is a very humble honest 3" pinoy...plus he get on his knees after every fight)...