Look on YouTube for tyrereviews. He does really good comparisons and the three best are PS4, Goodyear Eagle 5 or Conti 6. The Goodyear seems to be the best of both tyres. If you can hold off for now Michelin are releasing the PS4S in 18" which is normally the go to 19" tyre.
Further to this ^, Tyrereviews also has a video comparing the PS4 and PS4s (and another tyre I cannot recall ATM). His conclusion was that there are small but significant differences, with the PS4s being the better choice for steering feel, turn in and stability.
I've had PS4 for ~26,000kms and am generally impressed, especially with traction and wet grip. But I find them a little vague and floaty on turn in - I'd like something with more feel and bite - such as the PS4s. If these aren't available in my 18" size, I'll go for the new Goodyear F1 or Contis next time.