My graphics card Asus EAX1900XT currently runs at 500MHZ VPU clock (core) and 594 MHZ memory clock (according to ATI catalyst). But on the specifications, the values are 625 and 725 respectively. I looked in the overdrive section and it would only let me tweak it up to 621 and 720 respectively.
My question is shouldn't the graphics card be running at 625MHZ core and 725 memory clock normally...
In 2D mode, high-end ATI cards run @ reduced clock speeds to conserve power and save energy. Once you run a game, they are brought up to their specified speeds. In CCC, you will see that ATI overdrive enables the higher speeds in 3D mode only.
Get ATI Tray Tools, and you can make a graph, showing what the clock speed and when. The program will also allow you to decide if you want it to kill the 2D/3D speeds, and make the card run at rated speeds at all time.
Also, this is normal, ATI cards have that to save power, and produce less heat. In 3D application, the speeds are as rated.
I recommend you try uninstalling the Catalyst, use the latest drivers. Instead of the Catalyst run ATI Tray Tools.