You might want to consider getting one of the lower-clocked C2D's and just doing some light OC'ing. In another thread, I mentioned my plan to get an E6700, and was told to save my money and get an E6600, which will easily OC to over 3GHz.
If that's true, spending an extra $600 for the X6700 might not be worth it, because from what I've heard it likely won't OC much more than that lower C2D models.
If I was going to spend that kind of money for a CPU (which I might), I'd go for the QX6700, which potentially is 1.0x - 1.7x the processing power for the same money.