I've ridden both the Schwalbe Marathon Dureme 700x42 and Marathon Racer 700x40. Between the two, I give a slight edge to the Racer. I hit gravel quite a bit, and the Racer is better there. (Though the Dureme isn't bad.) I've never had a flat with either. The downside to getting tires this tough is that it deprives you of the opportunity to check out other tires. Until I wear these out, I can't really justify buying more.