hundredislandsboy :
I have an XFX GTS 250. It's already an overclocked 9800GT. The most you'll get is an extra 2 or 3 percent in terms of bumping up the GPU core/shader/memory and the gain is not noticeable.
The GTS 250 is a revised version of the 9800GTX+ , not the 9800GT.....
So just to correct what you said, since there is a significant difference in speed and power consumption....
The GTS can be overclocked to around 800/1207 <--------------- My GTS 250 (1GB)
Just download Ntune if you want to overclock your card, don't expect anything major and if you try overclocking past the above frequencies you will lock up the card or get a nice BSOD........