Wanted to mention 12.1 drivers scale well in CF.
I am running everything "Enabled" or "Very High" with ubersampling (retarded) off, and it runs great at 1920x1080.
8150 @ 5ghz, 6870 CF 1060core/1125mem.
Both cards 100% use with vsync off, with Vsync on I hold 60 fps with the occasional drop to 58/59 for a second.
If you have 12.2 or 12.3 I suggest you roll back to 12.1, as 12.2 and 12.3 cause global issues not just with the witcher on 6870s.
GG AMD.