Are you the same size and were you carrying the same amount (weight) of gear? I just did a tour with a small group. This one guy was on a bike with STI, and I was on a bike with bar ends. We rode together on our tour bikes before the tour, and I was WAY faster. Then when we loaded our bikes and went for the tour, he was somewhat faster. I think it was because he's a medium-size guy and I'm a small gal - he's much bigger than me. So the bike was relatively much heavier for me compared to my size.
Anyway, just a thought, and another data point.