@Radfoo:
Another reason for instability could be the motherboard. My original A1200 motherboard didn“t like my BlizzPPC, the machine simply froze or crashed regularly (sometimes it worked for a few minutes, sometimes for about an hour- but it always crashed sooner or later).
I got a new A1200 motherboard and the machine works fine for 5 years now. I guess my original motherboard was lacking the famous "timing fix".