1/2" makes a difference. You are evolving as a cyclist and wanting to be faster. That means more pressure on the pedals which translates to less on the hands and you can sustain a lower handlebar. The Roubaix has a long head tube by design. You can slam your stem down to the head tube and if still not low enough you can use an inverted stem on the order of negative 10-17 degrees or so. Many on this forum ride with a big bar drop and are strong cyclists. I am a decent cyclist and ride with a 2 inch bar drop which is a fair drop for a good rider. Racers many times run 3-4" drop. Reach is comprised of not only drop but horizontal reach. It is possible to ride with more drop but less horizontal reach for the same body position on the bike.
Hope that helps.