Dura Ace is lighter. Uses a lot of Titanium instead of steel or aluminum. Overall a lighter bike will accelerate faster and climb big hills easier, but once up to speed, weight does not really matter much. Dura Ace is typically used my racers and top level road riders. Sometimes 10-15 seconds over a 40 mile course can mean winning or loosing, and in that case, saving a little weight can mean a lot.