I have a Roubaix with the "Future Shock" front fork and the Zertz in the seat post, plus 28mm tires. It is a huge difference over my previous Roubaix without the future shock. There is one particular bridge that I cross every time I go out riding, and it has a textured concrete surface. Wth my old bike I would really feel a lot of vibration, but with the new Roubaix, I'd say it is at least 80 percent smoother. The downside is that it feels a little "bouncy" at the handlebars at times, but for this 65 year-old, It's worth it.
The future shock bikes come with three different weights of springs, and I am using the heaviest which is the black one.