i can definitely feel the difference between 23 vs 25 or 28 tires. I also notice a pretty drastic difference in 1 cm of reach difference. handlebar is just not something I really pay attention to, although I do notice flexing in my frame when I break 1 kW, and some of that is probably the handlebars/stem. I'm inclined to dismiss that as trivial loss though. not going to get hung up on 1% gains via equipment unless I get sponsored or something