I will throw my opinion out here, of course I am not an expert or elite cyclist by any stretch.

I honestly don't think the Domane and Roubaix are all that similar right off the shelf. I have ridden both recently as I am in need of a more plush ride. Getting older and have congenital narrowing of the spinal column resulting in neck pain with my Tarmac. I have rode both recently plus the Fuji Gran Fondo and the Felt Z4. I think the Roubaix is different from the other three. The Roubaix is very upright vs the others off the rack. I think the reason is that the seat tube is definitely more relaxed and results in a lower seat height vs the other 3. The other 3 are pretty similar as far as geometry and ride quality to me. The Roubaix definitely sits you back and upright. Personally I think the Felt and Gran Fondo are better values when considering components. I think the Domane was the most racey to me and probably had the least upright position. All 4 are very stiff as far as vertical compliance yet all 4 ride very nice, similar but a little better than my Tarmac, which I think is a nice smooth ride, just a very racey position. If the Z4 were more upright, I would buy it in a heartbeat. Great value.

For what I seek, the Roubaix is what I will buy. The fact that my LBS will take my tarmac as trade in for the F4 or Roubaix is a big plus for me. For me its not even close that the Roubaix is much more comfortable for me. might not be like that for everyone. I'd put the Domane in last place for what I need. However, if you want a bike that you can really go fast with as well as get a nice smooth ride, it might be your choice.