Assuming normal ambient temps (about 25), the mobo temp should be in the mid 30's, and the CPU in the 40's under 100% load. The CPU can take up to about 60 without harm, so that would lead me to think ambient temp can go up to about 40, maybe 45 and you'll still be ok, assuming good airflow of course.
Don't know about the x850, I'm thinking it may be more sensitive to warmer temps (it runs hotter than the CPU afaik). Hopefully someone else knows.
Mike.