Ortiz' mental state is the key in this one for me. He's an enigma. This fight, given the history, would definately ensure Ortiz would not give up, similar to the Berto fight. He seems to rise when the chips are down. Coupled with Ortiz's superior ability to box when he's on his game, he's definately got more dimensions to win this fight.
On the flipside, he could also come in too pumped, play into Rios's hands in a slugfest and do something stupid. The extra aggression in this fight would only boost Rios, who'd just keep coming and coming. Ortiz by a very close UD or possible SD.