Well Andy, you're correct. And to answer the original q, I say go with wider tires, difference between mountain knobby tires and slicks is going to be substantial all by itself, and that slightly narrower tire would not make much of rolling resistance improvement over those that are a bit wider, bit it would be more substantially rougher to ride. So I vote for 1,5", although that is also on the limit for what I consider a usable city tire - on the skinny limit that is.