"A 23 will have less rolling resistance", not neccessarily correct. For otherwise identical tyres, a 23mm will have greater rolling resistance than a 25mm, if they are inflated to the same pressure. A rider that has become used to their 23mm inflated to 120psi, could reduce rolling resistance and improve ride quality by going to the exact same tyre, but in a 25mm. They would still inflate to 120psi. A smaller tyre has it's performance advantage only at significantly higher tyre pressures. If you're part of the 98% of us that don't ride competitively, you would quickly realize that a 23mm tyre at 140-150psi isn't a very welcome companion over many miles and hours. And, if you're presently riding a 23mm at lower pressures (120-130psi), you would improve your life by going to a 25mm in the same tyre and inflating to the same 120-130psi.