I've actually found that leveling is ridiculously slow if you try to "complete" every zone. From an early level I completely out level the trash mobs to the point of not being able to loot them and getting little or no exp from them. The quests still give exp but that's it. Being like 5-8 levels above the zone you're questing in slows everything down, and makes you wish you just would go do other higher stuff and skip content.