I'm glad there are some tyre threads going, as this would be something I am looking to replace on my Zed and would like some feedback.
I've always had Michellin PS2's but it seems that nobody even mentions them anymore.
In regards to buying part worn tyres, obviously a lot of people would never entertain it but I have done this in the past. I had 4 x PS2s running on my E36, I got them with 6mm of thread and they lasted me years with no issues, but like you say it is a risk as you dont know how long they have been laying around, etc.
It would be nice to know how long the Goodyears last, I had the Goodyear Eagle F1's also back in the day, they last me 6 months and I couldnt justify buying them again.
Kwik-Fit down here will not touch anything not supplied by them, Pro-Tyre will do it but it depends who you speak too and what mood they are in. I've always got my tyres from Black Circles.