Use ATI Tool ( found here: http://www.techpowerup.com/atitool/ ) and use the find max overclocking button to get the max your card can do. Radeon 9550's seem to be quite random in their top speeds. I only got 445/209 out of mine but I've heard some people get 500/500 out of them. If you start getting an extreme oveclock make sure you have a good fan on it to keep it from over heating.
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