I don't know about CX tires but the difference between studded Schwalbe Marathon Winter tires and Conti GP4000s is about 50 vs 40 Calories/mile.

I wouldn't want to commute regularly on knobby tires. I have some 40mm Schwalbe g-one's at the moment that are decent on gravel and feel smooth on the road. If I was only riding on the road I'd go back to the GP4000s.