No comptetition..the 8600 GTS is not in the same league.
The weak spot with the 8800GS and cards in the same class, is its 384MB of 192-bit memory. On lower resolutions this isn't a problem, however if you crank up the detail and resolution you'll see a large drop in frames.
On that basis the choice for me would be between a 9600GT and faster 8800GT. Both offer 512MB of 256-bit memory.
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