I have made a X-Y chart with this info, plotting price vs. performance. I uploaded it here:
http://bp2.blogger.com/_AIJ1WOm9bKQ/SC9p89QuLqI/AAAAAAAAABA/nmbUpekA9nE/s1600-h/Price+Performance.PNG
The red spots are the hardware that is the cheaper for a given performance, and simultaneously the fastest for a given price.
It shows only four combinations that are worth of a buy:
Geforce 8800 GT OC (512 MB) E2160@2.41
Geforce 8800 GT OC (512 MB) E6750@2.67
Geforce 8800 GTS OC (512 MB) E6750@2.67
Geforce 8800 GTS OC (512 MB) Q6600@3.2
the FPS are plotted with the Geforce 8800 GT OC (512 MB) E2160@2.41 as 100%.
It shows that spending two times his price you can only but less than 30% more performance.
and probably is harder to justify spending more than the price of Geforce 8800 GT OC (512 MB) E6750@2.67. You can spend 100€ more, for only a 8% more speed.
The green points are roughly in the same place, they are the Geforce 8800 GTS OC (512 MB) E6750@2.67 and the Geforce 8800 GTS OC (512 MB) Q6600@3.2.
I would buy the 8800 GTS 512 Q6600. Why? Is almost the same than the lightly cheaper and speedier 8800 GT 512 E6750, but it contains 4 processors, from which future games can take -Probably- advantage.
That chart shows much more readable information that the tables in this article. Any article of this kind must include this kind of chart.