Just to add another twist...
It kept reporting 1067Mhz when I paired the 8GB OWC DIMM with one of the 2GB Apple DIMM's. No black screens.
I happened to have a 4GB PC3-12800 laying around, so I installed the OWC 8GB DIMM on slot-0 and the 4GB in slot-1.
Both reported at 1600Mhz, and black-screen as soon as I started playing a Flash video.
It kept reporting 1067Mhz when I paired the 8GB OWC DIMM with one of the 2GB Apple DIMM's. No black screens.
I happened to have a 4GB PC3-12800 laying around, so I installed the OWC 8GB DIMM on slot-0 and the 4GB in slot-1.
Both reported at 1600Mhz, and black-screen as soon as I started playing a Flash video.