Trusted Reviews looked at the Intel Core 2 Duo 'Conroe' E6400, E6600, E6700, X6800 processors

For comparison, we have bought in a Pentium 4 670 (1 x 3.8GHz, 1 x 2MB), a Pentium 4 Extreme Edition 955 (2 x 3.46GHz, 2 x 2MB), Core Duo T2600 (2 x 2.16GHz, 1 x 2MB), Athlon 64 5000+ (2 x 2.6GHz, 2 x 512KB), Athlon 64 FX62 (2 x 2.8GHz, 2 x 1MB). And just for fun I overclocked the FX62 to 2.92GHz, for a clock to clock comparison to the X6800.

Intel Core 2 Duo 'Conroe' E6400, E6600, E6700, X680 Review