PowerAu

this is because 250 GTS will be replace the model of 9800GTX
250GTS and 9800GTX are using same GPU chip which G92.
however 250GTS core speed and memory speed is much better than 9800GTX...
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NVIDIA 9800 GTX

Specifications
Core Clock:         675 MHz         Memory Clock:         1100 MHz
Memory Bus:         256 bit         Memory Size:         512 MB
Memory Type:         GDDR3         Interface:         PCI-E  ?
ROPs:         16                    
Shading Units:         128                
Graphics Processor
GPU:         G92         Process Size:         65
Transistors:         754M         DirectX:         10.0
Pixel Shader:         4.0         Vertex Shader:         4.0
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NVIDIA GTS 250

Specifications
Core Clock:         738 MHz         Memory Clock:         1100 MHz
Memory Bus:         256 bit         Memory Size:         512 MB
Memory Type:         GDDR3         Interface:         PCI-E  ?
ROPs:         16                    
Shading Units:         128                
Graphics Processor
GPU:         G92         Process Size:         65
Transistors:         754M         DirectX:         10.0
Pixel Shader:         4.0         Vertex Shader:         4.0
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hope that will help. i will say 250GTS is better buy than 9800GTX