I've found that mage damage seems fine - Maxed out destruction, +100 magic damage on each dual wield weapon and 100 int, and it all seemed to stack properly. Never used 'way of the battle mage' though, as I don't like it's weakening effects - I spent the skill points on extra magic attacks instead (otherwise I wouldn't have been able to max out all four - magic blast, firewall, fireball and magic missile).
