I went through this dilemna not long ago. When I bougth my boxster off my dad it needed new tires.
He had been running the OEM tires - Pirelli PZero (N3). I had driven the car a lot before I bought it and alwyas said it was the best handling car I'd ever driven. I dind't wnat to mess with what i knew worked - so I bought the same thing instead of switchign to PS2s.
I love them. they stick like crazy. i'm sure the PS2s are great too.
My opinion is that unless you are tracking the car regularly, or are REALLY sensitive / in tune with your car - you probably can't tell a big difference between the various tires - assumign you are comparing apples to apples.
PZeros vs PS2s... can you really the difference? I'm sure there are people who can tell the difference. I could probably tell the difference if you bolted on set on, let me drive like nuts for a little, and then switched them out on the track and I got to drive the next set back to back.
but most of us don't do that. we buy a set of tires, drive them until they are bad/need replacement, and they buy more tires. anything you buy will probably be better than the worn out set you are replacing and you'll be happy.
a lot of this stuff is relative.
it's like TVs. go to Costco, Best Buy - wherever they have the TVs all lined up and you can see the microscopic differences between the various brands. once you settle on one, and get it home - you just see yours. and you like it.