What to watch for:

• Pacquiao has not stopped an opponent since Miguel Cotto in 2009. He has still had decent power, hurting foes with some degree of regularity. But he doesn't have quite the same shocking stopping power at 147 and above. He should have enough power to hurt and back Rios down, but if his power and Rios' chin add up to an inability to stop the freight train, does he still have the reflexes to survive a firefight?
• Rios isn't hard to figure out. But how will 147 suit him? Will he have good stamina? Will his chin hold up? Does he have enough power to complement the volume?
• Is Pacquiao done? The Marquez knockout was scary. People forget that, but it was actually a frightening moment where he didn't move for a few minutes and had been caught amazingly clean. There's a long list of fighters who never recovered from something like that and Rios has the game to show if Pacquiao was broken forever in that moment.