As a sch in coil id say the only real way to go is pure mind. Some people have talked about adding int for extra crit chance but the trade off is way too high. As for piety, piety is a strong attribute but no matter how much mana you have there will always come a point in coil where the bard needs to do his mana song for both the sch and whitemage. Thats why bards are so valuable in these groups.