In my experience larger volume tires do make a big difference, especially with smoothing the small bumps and vibrations. However, there are many variable between tires (construction, quality, etc.), not to mention the frames and wheels, so the only way to really know if the Domane will handle the small bumps and vibrations as well as the GF01 would be to take it out on another test ride with the 28 mm tires. Can the bike shop just swap out the wheels for you and let you go on another test ride?