i actually have two xfx 6870 black edition and ran into some trouble lately (after messing up my driver installation and even completely redoing the system and setting up fresh drivers
so until 2 days ago i had them running in crossfire mode with msi afterburner set to 1050core/300memory, no voltage adjustment (+ an additional 5870 at 950/300 with stock voltage).
if i try this now, it does not work, the system freezes right after hitting the apply button in afterburner or after a couple of seconds when i start mining.
i have tried catalyst 11.5, 11.5b and 11.6. I would really love to hear ideas why it now does not work, while it did work a couple of days ago.
also tried afterburner 2.1, 2.2beta3 and beta4 (which runs fine at lower coreclocks right now).
i must also say, that with 1050/300 my system used about 50 watts less then now (1008/575)!
If anyone knows more about working voltage settings or what voltage increase helps stabilize the system...