As I said several days back, my friend and I brought our M3 to "fun spot" for comparison and did some aggressive driving. Since our cars are quite similar, I say it's fair to compare.
Friend's: PS2 800mile + 2months old
2009 M3 coupe with Eibach Springs and ZCP wheels
255/35/19 and 285/30/19
Mine: PSS 250mile + 7days old
2011 M3 coupe with ZCP everything stock,
255/35/19 and 275/35/19
PSS definitely has stiffer sidewalls and stickier compound than PS2, and I guess these make PSS easier to drive in extreme condition. Difference between them was very clear when getting out of the corners; PSS has more kick from the rear where PS2 rear tires went sideways. Turning in also feels nicer than PS2. I was being able to go with confidence maybe because of stiffer sidewalls, or its compound, I don't know. PS2's softer sidewalls make street driving quite comfortable, but in the track, I didn't like it so much. Only downside of PSS for me was difficulty of finding its limit. Somewhat I was not very sure where the limit of PSS was although PS2's was easy to find. PSS sometimes gripped much more than I expect, sometimes as much as PS2, so I perhaps have to get used to how to use it.
Their tire wear seemed the same. It's clean and not greasy at all. Since we just drove our cars slightly over an hour or so, I couldn't find a big difference. Of course both tires looked healthy and still had enough rubber. Maybe we didn't push tires too hard, or we are too gentle to push tires to its limit, who knows. However, if we drive them on the track at the same speed, then PSS may lasts longer, IMO.
If you want non-R compound track tires, I strongly recommend Pirelli PZero Trofeo. I have driven it only once, but I was seriously impressed. Even old Pirelli PZero Corsa System will do much better job than PSS on the track. PSS is indeed better than PS2 in almost every aspects and might be the best street tires now, but this doesn't mean PSS is the best tire on the track.