CC is playing for the yankees. His innings pitched is going to go down. Yankee pitchers don't pitch more then 7 innings...ever. Often they don't pitch more then 6. Its just their philosophy. That means you are talking about does his wins and losses outweigh peavy's ratios. In a H2H league i take ratios over w/L any day of the week.
While it's true that CC won't be worked as rigorously as he was in Milwaukee, CC should still go deep in games.
Back on point, I'd take Peavy. If this were a roto, it would be closer, but personally I'm not that keen on chasing wins even if losses come in the equation. Sabathia won't be quite as lights-out when he was pitching in the National League naturally now that he's on an AL side. CC will still be very good, but I think Peavy on a full bill of health, will have better ratios, especially if he stays a Padre.