To be honest, artifact traits / spells are really usefull and it's hard for the mace to be better than the artifact weapon. That said, my sham only has a 768 artifact weapon, but I got him a nice 870+socket mace, that gives him a nice +6700 intelligence and +800 secondary stats. This is an average +40% dps if we only count stats. But artifact weapon and traits actually increase dps by a lot (at level 19, as it is for me, I'd say it could give +20% dps ?). What I did is I created a macro to switch weapon (as you can do this while in combat) and I'm switching everytime I wanna use artifact weapon's spell (otherwise I play with mace).