If you're going with a bigger sidewall tire, I would recommend adjusting the tire pressures accordingly using
this calculator.
I had my 205/50R16 tires at the OEM 39PSI front and 36PSI rear and was wondering why I could not feel a difference in ride.
For the same load rating, the calculator suggested 31 PSI front, 28 PSI rear using my 50 sidewall tires. I lowered them to 33 PSI front and 30 PSI rear and I could feel a difference right away.
For ride quality, I can't comment on the MK8 Fiesta, but if it follows the same engineering logic than the MK7, it is probably over-damped (meaning, dampers have too much damping force applied either rebound or compression) from the factory.
If you're interested in coilover with adjustable damping, keep in mind that the springs with those kits will be significantly stiffer than stock, but you'll be able to adjust the damping to your liking. Many people on these forums have reported that some coilovers have increased the ride quality (I have seen good comments on the BC coilover series). Adjustable damping does not equal better damping, however, so keep that in mind.