To be clear, my "heavy steel bike" is a Bianchi Vigorelli with Reynolds 631 and Ultegra/105 mix, so it weighs in around 20-21 lbs. It's not a tank like a Surly Cross-Check or LHT or Bianchi Volpe with Tiagra or lower-end components. In contrast, my carbon bike weighs about 16 lbs. Granted my carbon bike has upgraded wheels and a Campy Chorus groupset, but any stock carbon bike in your size should weigh about 17-18 lbs if it has an Ultegra/105 groupset. Once you start doing longer test rides involving climbs, you should totally feel the difference between a carbon bike and your Dolce.

Before you completely rule out "comfort" bikes, you should take a few of them on longer test rides. By "comfort" I'm guessing you mean a relaxed geometry with a shorter top tube. Keep in mind that more bike companies are offering relaxed geometries for riders who don't ride very much and probably are not comfortable with an aggressive geometry, where you're totally stretched out over the top tube to get into the most aero position. But relaxed geometries are also better for sportive or endurance riding, where you're in the saddle for 5+ hours. If you want a bike only for shorter rides (up to 2-3 hours), then an aggressive geometry where you're stretched out may be fine, but if you want to start doing longer rides like century rides, where you'll be in the saddle 7-10+ hours, then the more upright position is more comfortable once you reach hours 4-5.

Keep in mind that you can always make a bike with a more relaxed geometry (i.e., with a shorter top tube and tall head tube) more aggressive by swapping for a longer stem and using a negative angle, but it's a lot harder to make a more aggressive bike (i.e., with a longer top tube) more relaxed since you'll compromise the handling with a really short stem (<70 mm) and a really steep angle.