I had to start this topic because I would say 75 percent of the people I talk to that are going for Floyd tell me he is going to knock him out.
(Quick Disclaimer to avoid flaming: I pick Mayweather by decision, but I give Manny a real good chance to outwork Mayweather and possibly get a decision)
My point is Marquez is an offensively minded fighter with a good defense and counters, while Mayweather is a defensively minded fighter with a good offense and counters. Marquez had his feet planted with forward momentum for most of Marquez Pacquiao 4 because he was going for the KO and that setup the big right hand he hit him with on multiple occasions btw in the 4th fight, the last one was just perfect which got him the KO.
I do not expect Mayweather to plant his feet and throw a big power punch like Marquez did. Marquez will lunge forward with his counters and throws big powerful punches, while Mayweather sits in a defensive position and pushes forward enough to land his punch's, but not with offensive power in his mind like Marquez.
The last KO mayweather had was with Ortiz which was standing right in front of him, and the one before that was Hatton that I believe happened after repeated punishment from Floyd's left hooks. I can see Manny having the same fate, but not a one punch KO from Floyd. I'm not saying that its not possible for Floyd to throw a one punch KO, but he would be risking more to throw a big power punch and he is not going to do that because he is defensively minded.