This is regarding weird issues with MSI Afterburner's unofficial overclocking. Prior to apply these settings, I had successfully managed to overclock my Sapphire 6850 to 850Mhz core clock and 1150 memory clock before the card started acting up.
UnofficialOverclockingEULA: I confirm that I am aware of unofficial overclocking limitations and fully understand that MSI will not provide me any support on it
Since my core clock would not physically go higher than 850Mhz, I knew I had to modify the MSI Afterburner CFG. Upon applying the above settings and then doing any changes at all to the core / memory clocks, the screen would start flickering. I undid the unofficial overclocking CFG settings and all is back to normal again.
My experience as explained above freaked me out a bit... thought I fried my card... is there any other tool worth considering to go beyond the 850Mhz cap? I understand from reviews out there (most notably HardwareCanucks.com), that the 6850 can achieve 890Mhz core clock and 1192 memory clock on stock voltage.
EDIT: Don't hate on me for bringing this up, just sharing my experience. Looking to see if others experienced screen flickers by simply unlocking the Unofficial Overclock.
Not every 6850 will be stable at 890/1192. Every card is different, some will be able to overclock more than others. You can try boosting the voltage ever so slightly to see if you can get it stable at higher clocks (assuming your card has unlocked voltage control).
Really though, you probably aren't going to squeeze much more performance out of that card. The 6800 series cards were not the greatest overclockers, and pushing your clocks higher will likely only yield very small framerate increases, like 1 or 2 FPS. It's probably not worth risking damage to your card to go past the official limit.
As per your above statement, "It's probably not worth risking damage to your card to go past the official limit", yes I agree with you. I'm not going to increase the voltage on the card, I'll just stick to overclock on stock voltage.