I think the main idea is that the narrower the tire, the less rolling resistance you have. That said, once you go to a 23 mm tire, it's more important to have a good surface--enough grip so you don't slide out. I've been riding Hutchinsons--their Fusion Team has different grades of rubber extending from the center of the surface that contacts the road, so that the grippier part comes into contact when you're cornering at speed. They feel much more secure to me than anything I'd ridden before. BTW, I've been getting closer to 3,000 miles before having to replace.