You should be able to shred the breast after they reach 165°F, or maybe a combination of shredding and chopping. Taking the breast to 180°F or 195°F, even adding the finishing sauce the meat texture may be stringy. The dark meat you can take to 180°F to 185°F, some cookbooks state that is the prefer temperature for dark meat. If you smoke the breast on one rack, and the leg quarters on a second rack, you can take the breast out when it hits 165°F, and continue to cook the leg quarters until they reach the preferred temperature.