+ATK/-RES or +SPD/-DEF Zelgius

plus attack for power

I'd say go for the increase of Atk. Any mage he fights, he wants to 1 shot. Combining it with QR, he's able to essentially add 6 extra atk. That's a good set. Extra cool down when he's defending, extra when he's attacking, guaranteed follow up both ways(as long as he stays above 70% HP for QR) You have very little need of the extra speed with that set. Hone Armor can bring him up to 39, which is enough to avoid a LOT of doubles outside breakers and Bold/Venge fighter and Brash Assault.