He is a genetic freak. you can't really call it the 'extra' weight. because when he added those pounds he pack on muscles on his massive calves and his back. thus making his legs more stable and explosive. and thats where the power comes from. it's called kinetic linking. unlike most guys who moved up in weight u see them with bigger arms, chest and often a flabby stomach. with Pac he has adjusted very well by packing those muscles on the right places. I think his chin isn't a suspect. Marquez hits hard. Morales hits hard. and so is Barrera. they may not be as physically imposing and as brute as Ricky but if we're talking about punching power they arent really significant differences. Now IMO the key here for Ricky is to 'bully' Pac. Not to knock him out with a single punch.