I have a 12 Focus SEL and a 13 ST. The ST is quieter going down the road than the SEL. When we got the SEL I though the quietness of it was amazing for a compact car.
There is a 5 mile section of road that I travel every day going to work, it has to be in the too 10 worest roads in Mass. Anyway, the PT Cruiser the ST replaces would jar your eyes it was do bad on this road. The ST and SEL just float over the pot holes and broken pavement with no jarring or bottoming.
The suspension is stiffer on the ST than the SEL but not by much and much much less than I expected.