I saw a post a few days ago on this site where someone did this exact thing on a 5850 or 5870. He saw drop in temps, I believe for him it was about 5C. Another posted that he didn't have any change.
Keep in mind. Load temps will be control by the fan speed. If the AS5 does help, you may not notice any load temp changes at all, but instead, the fan speed will drop instead.