Followings are the overclocking profiles of my ASUSTeK MATRIX HD5870 P/2DIS/2G

I generally flighsim under 970MHz setting but sometimes further OC to 1000MHz as follows:

Fan speed varies from 40%, 50%, 70% to 100% according to the temperatures set.

Both profiles are not aggressive and quite stable under my system.  However, I prefer 970MHz more since it keeps the noise of the fan to a lower level most of the time.