This is how I clocked my 9800GT which is AFAIK a rebranded 8800 (G92 chip): GPU 624 MHz RAM 900 MHz Shader 1809 MHz. http://www.techpowerup.com/gpuz/kh4dp/

Think I had some stability problems so I went back to stock GPU 600 and Shader 1792 or so.

Hope this helps.