I think Shane will lose as well, but I also think he'll look better than he did vs Mayorga.
The difference between Mayo and Margo is speed. Mayo was quick enough to be physically on top of Mosley all night, using his strength to wear him down and keep the fight at his distance. Margarito is too slow to get this close to Mosley. The distance will favour Mosley, who also has more experience than Cotto, and should have the IQ to clinch and separate if it gets close. I see Mosley looking good through 6, doing the Cotto strategy better than Cotto, and not getting caught up in exchanges, and controlling the distance.
But like you guys, I see Margarito eventually wearing him down, and stopping him late in the bout. I don't this will be the wipeout that you guys do. I think Mayorga was just a bad match-up for him, coming off a long layoff, and he used a bad gameplan. This bout the gameplan is simple, he's active, his opponent is extremely slow and plays to Mosley's strengths. A prime Mosley beats him, this Mosley puts out a strong effort, but gradually fades and gets stopped.
Mosley's power is far too little to discourage Margo, I'm not suggesting he'd do any damage, just bank early rounds.