http://www.sharkyextreme.com/guides/WCPG/article.php/3636096
Weekly CPU Prices - Week of October 2, 2006
October 4, 2006
Dual core AMD Athlon64 and Intel Core 2 Duo CPUs, sorted by price...
$160 Athlon 64 X2 3800+ 2.0GHz AM2 Retail
$175 Athlon 64 X2 3800+ 2.0GHz S939 Retail
$183 Core 2 Duo E6300 1.86GHz LGA775 Retail
$185 Athlon 64 X2 4200+ 2.2GHz S939 Retail
$186 Athlon 64 X2 4200+ 2.2GHz AM2 Retail
$224 Core 2 Duo E6400 2.13GHz LGA775 Retail
$227 Athlon 64 X2 4400+ 2.2GHz S939 Retail
$234 Athlon 64 X2 4600+ 2.4GHz S939 Retail
$245 Athlon 64 X2 4600+ 2.4GHz AM2 Retail
$280 Athlon 64 X2 4800+ 2.4GHz S939 Retail
$318 Core 2 Duo E6600 2.4GHz LGA775 Retail
$524 Core 2 Duo E6700 2.66GHz LGA775 Retail
$569 Athlon 64 FX-60 2.6GHz S939 Retail
$965 Core 2 Extreme X6800 2.93GHz LGA775 Retail
If I was going to buy any of the Core 2 chips, I'd only consider the chips with 4MB cache...
Extreme X6800 2,933 MHz x11 266 MHz (FSB1066 QDR) 4 MB cache
Duo E6700 2,666 MHz X10 266 MHz (FSB1066 QDR) 4 MB cache
Duo E6600 2,400 MHz X9 266 MHz (FSB1066 QDR) 4 MB cache
Duo E6400 2,133 MHz X8 266 MHz (FSB1066 QDR) 2 MB cache
Duo E6300 1,866 MHz X7 266 MHz (FSB1066 QDR) 2 MB cache
...so that's basically the E6600 and up.