personally, i'd forget the QX6700, and compare equal processors. On Newegg, for instance you have:
Core 2 Quad Q6600 for ~$530
http://www.newegg.com/Product/...x?Item=N82E16819115017
and
Xeon X3220 for ~$575
http://www.newegg.com/Product/...x?Item=N82E16819117127
now, these are both Kentsfield core processors, and have absolutely identical specs and are basically identical in almost every way.......... but keep in mind, the Xeon is a server chip, so it is most likely more conservatively rated (higher OC potential, possibly).... but seeing as these are all Core2 based, i'd probably tend to think of that as much less of a factor than it was in the past with the Netburst chips........... is it worth the extra $45 for the peace-of-mind associated with a server chip (which in my eyes these days is basically nil)? Regarding the Core2 extreme QX6700, other than the higher clockspeed, the multiplier is unlocked. This can allow for better overclocks for reasons that i'm not going to get into, it's easy to google it.