I am running 2 XFX HD 6870s in crossfire x, and they run at about 85C when maxed out doing bitcoin mining, and I'm worried this is too hot. I can't find any spec sheets from AMD stating their safe operating temperature range. how can I find this information? Google has not helped much.
85 degrees is safe for full load, if a bit hot. GPUs are designed to take higher temperatures, as long as your temps don't creep up into the mid 90s or higher you should be okay. However, GPUs will last longer if you do keep their operating temperatures lower. You could use MSI Afterburner to set a more aggressive fan profile. The default fan settings on most cards tend to be inadequate if you push the GPU to full load for extended periods, as manufacturers tend to focus more on making their cards quiet rather than ensuring the best cooling. Setting the fans to speed up to 100% at a lower temperature (say 70-75 degrees or so) may help, by default the fans usually won't speed up to 100% until the GPU temperature hits the mid 90s.