You might want to post your question here as well - http://forums.techpowerup.com/
There are a few posts there with people finding the same thing that you are...memory that is underclocked for their 9600XT.
Maybe your drivers are not allowing you to change the settings at all. I saw in the latest stable version of ATI Tool...the following fix:
- Removal of Catalyst overclocking lock for 9000/9200/9550/9600 series.
Finally, another post mentioned the following:
1. Run DriverCleaner and then install the latest normal drivers, nothing tweaked or modified.
2. Scan for artifacts at the stock settings for awhile to make sure the heat behaves.
3. If all is good so far, go through the normal routine with ATITool, but only up to about 550/330 at the most. I say that only because I destroyed a 9800PRO (Hynix vram) last year with ATITOOL.
4. If you want to try for more speed, definitely get some good ramsinks and a good GPU cooler. After you're confident its fine then you can mess with different drivers, etc.
You might want to be careful with the overclocking though since it seems to be giving you fits. I don't want to see you frying your card...
In the end, my bet is it is the card and cheap memory and there is not much you can do other than to live with it or return it.