Ah, now i know what you mean with underclocking
I can try. I have all the tools installed and could underclock my ati as much as possible. Haven't tried that yet though. But i will restart and patch my BIOS now...
So, back again.
I tried to underclock my 5670 as much as possible. The slowest possible setting was around 100/100. Going deeper isn't possible, because the screen is so corrupted that i can't even log in.
Anyway, underclocking doesn't work either. Still the same problems with graphics.
are you willing to test to flash your graphics bios to "disable" the power saving mode on your 6850?
Btw, there are some people in the apple forums that experience the same issues when using chrome, html5 or even youtube... making their screen garbage.