Re: Intel Core 2 Duo E6600 - Intel Core 2 QX6800
The difference between the Q6700 and QX6800 is that the Q6700 is 2.66ghz, while the QX6800 is 2.93ghz stock, and that the QX has an unlocked multi while the non extreme version doesn't.
The Extreme Edition is like a Black Edition AMD processor.
Either way for $200 you could get a Phenom II x4 965, and have $50 to spend on beer while you enjoy not only better performance, but better overclocking potential as well.
Of course this would require upgrading the motherboard as well, and somehow I doubt you'd even consider a Phenom II.
If I were you I'd just get the 6700, save a few bucks, and overclock via FSB