Since I do not race, the way I measure performance when I try different things is to ride a particular ride. It is 36.5 miles with several thousand feet of climbing, and a lot of twists and turns. I time the ride with each setup, adn repeat the setup a few differnet days. Then I note the elapsed ride time, and the overall ride comfort. Since most of my rides are of this length or longer, being more comfortable probably has more of an effect on performance than it would on a flat out full speed short ride. On my rides, the times were on average the same with either tire setup. The biggest difference for me is that with the 25mm tires at the lower air pressure, I feel like I could continue on for much further, while with the 23mm tires at the higher pressure, I feel more tired and certainly more beat up.