I used to have 23mm Gatorskins, then switched to 25mm. I never really noticed much of a difference. In general wider tires are supposed to be faster and more comfortable, I think, because they have a larger contact patch and absorb vertical movement better so you don't lose forward energy when you hit bumps or uneven pavement. But I don't think 2mm makes that much of a difference. And the air pressure in the tires also has an effect. Many people put more air in than is necessary.

I recently replaced 25mm Mavic tires with 25mm Conti Grand Prix 4000, and I notice more road buzz from the new tires than the old ones. I dropped the psi a bit and that has made a difference.