Best I've hit on my hybrid is 34 mph on a mild downhill, and about 20 mph on the flats, though that didn't last for too long before I was sucking air. I'm running 42-11 gears on Vittoria Randonneur Pros in 700x32. On the downhills, my gears aren't high enough, or I'm sure I could go faster. Nice adrenaline rush, but that nervous fear factor creeps in sometimes especially on curves.