When I got my ver8 longblock from Japanstar it had range 8 irridiums in it. I never had any knock until a fuel tuning session inadvertently induced massive lean knock at 6300 RPM. Never had any knock since. Although my timing is certainly on the conservative side for a spec-C engine. This behavior didn't change AT ALL when I went to range 7 coppers (because I'm still just running the VF36).
I find it curious that the previous Japanese owner was running range 8 plugs. Maybe they know something we're just starting to clue in on?