Except everyone gets 100% crit pretty much on Rageface during his Facerage and Lava burst hits only slightly higher than a shadowbolt (my own ele's are typically around 30-35k). The best spec for the dogs is by far an Arcane mage, as they hit consistantly high and dont need any prep (i.e. they can just hit it with an Arcane blast without having to get dots up or hit another button to make their spell hit harder).
@ OP, as stated above, only the Felhunter or a destro lock could potentially break Rageface without really high end gear everytime. You would be better off with another class on the dogs if possible.