Without a doubt go with the Intel® Core™ 2 Duo E6600. The Intel Core 2 Duos were outperforming much faster Intel Pentium processors. As I just said on another thread I remember seeing benchmarks between the Intel Core 2 Duo E6400 at 2.13GHz and the Intel Pentium® Processor Extreme Edition 965 at 3.73GHz. In that comparison the Intel Core 2 Duo E6400 outperformed it in 16 of 20 different benchmarks and was only barely outperformed on the other 4.
Intel Enthusiast Team