I just did a couple of tests before and after with my crossfired 6850's.
Not much of a difference, but a tiny improvement.
Unigine Heaven for example;
before 12.11 - fps 80.9, scores 2039, min fps 23.6, max fps 145.8
after 12.11 - fps 81.1, scores 2044, min fps 32.0, max fps 146.4
Few of the games I ran there was 3 to 5% increase in average FPS.
But this could be due to crossfire, plus 12.11 isn't promoted as drastically improving 6000 series cards.
Just thought I'd share. I'll keep it installed since there is some improvement