If my ward is reducing 120 pts. of damage, how does that compare tot he block skill? What I mean is, what would be an approximate block skill plus shield material and smithing level's worth of damage reduction?

The reason I ask is, I have a pure mage who I want to turn into a spellsword, but I don't have a lot of perks. My greater ward spell does about 120 pts or so of damage reduction. Is this a viable alternative to a shield?