Comparing these to previous tires:
Michelin Pilot Sport 205/40-18, Ford Fiesta ST
Michelin Pilot Sport 4 205/55-16, Ford Mondeo 2.2 TDCi
Nokian Hakka Blue 205/55-16, Ford Mondeo 2.2 TDCi
Federal 595 RS-R 205/50-15, Ford Sierra Cosworth 4x4
Toyo Proxes T1R 225/35-16, Ford Sierra XR4x4, Ford Cougar
As you might have guessed, only the PS4 in the Fiesta is really comparable on most conditions, but I could mention that the levels of grip seem to be far out of reach of Federal & Toyo on the dry, and incomparable in the wet.
In noise & comfort the Potenza Sport in this size loses to the PS4 in 16" but ties with it in 18".
When the tire is cold, it doesn't grip. Good news is that it only takes a few kilometres to warm up, as long as the outside temperature is above 10 °C. At normal driving temperatures, grip is equal or superior to that of PS4 even in the wet. When the traction is lost, it feels a bit sharper than with the Michelin. PS4 might be a friendlier tire all around, but PS feels like it has an advantage in traction. Will update this after a trackday.