I've been quest boosting my 64 shadowpriest the passed few days with my affliction lock 70 and I've found it to be a bad form of leveling tbqh. Tracking experience per hour with titan i find that my experience is reduced by around 50% even with only a 6 level difference. The slightly faster quest completing doesn't make up for the reduced experience per kill. I think I'll have to resort to kicking my lock out of the group and just tagging mobs with improved curse of shadows for the 13% bonus damage. Hope that works, I'll have to see when I get home.

I don't plan to boost within the group anymore unless it's for instances. As for boosting out of the group, a melee class like a ret pally, warrior, enhancer, rogue, ect will certainly still do great with a healer.

Also, dark pact + mana feed is really a bad way to go. You lose out on the really good deep Demo talents when they are considered the only reason to go that deep into demo in the first place.