On the open road, there is more to consider than weight and rolling resistance. I went from 23 mm on a narrow rim to 25 mm on a slightly wider rim and the difference in comfort and confidence has lead to a noticeable increase in overall speed on 20-100 mile rides. Road buzz was reduced and the bike feels much more secure on curves and sketchy surfaces, such as sand kicked or washed up from a shoulder or old rough pavement. In short, the tires might not be faster, but I am because my hands aren't numb and I can keep my speed up in situations where the 23s might feel squirrely.
BTW, on my long rides (50-100 miles) the difference in speed between my road bike with 25 mm tires and my flat-bar mutt bike with 32 mm tires, of the same brand and model, is between 1 and 2 mph on the same route under similar weather conditions. Even with the same bike and the same tires, my rides can vary by 1 mph or more because of slight differences in weather, hydration, or how I'm feeling that day.