My road bike currently has 25s (Bonetrager RaceLites) and I decided to go with 28s (Schwalbe Marathon Supremes) on my winter commuter cyclocross bike for my 20 mile round trip commute. I don't notice much of a loss in speed and they seem to be a little softer and more forgiving with better traction in the wet. Although the Supremes do kick up a lot more spray.