I've got an Infinito Ultegra. Its a great bike. Its not really in the same category as a Roubiax/Domane. The Roubiax/Domane both have a rear suspension/isolation system to absorb bumps, the Infinito does not. If your main roads are particularly bad, the Roubaix/Domane will be your best bet. That said, the Infinito is an incredible ride, I find its a pefect mix of speed/stiffness and smooth ride. I have ZERO regrets about the bike. The Infinito is basically a race bike with slightly relaxed geometry. Its a gorgeous bike, and rides like a dream. The wheelbase is a little longer, and its incredibly confident on descents.

I would seriously consider waiting for the new Infinito CV frame, its supposed to include much better damping. The price you're showing there is full list, and I wouldn't pay full list now, knowing that an improved frame will be out in 2-3 months. I purchased my Infinito Ultegra on sale for only a few dollars more than the 105 price you've got there, so definitely negotiate.