INTEL XEON CPU QUESTION

what is the difference between this chip:

Intel Xeon X5355 Quad Core Extreme, Socket 771, 2.66GHz, FSB 1333MHz, 8MBCache, RETAIL + Passive HSF

and other Xeon chips? What motherbaords do these chips fit on?

Is this Xeon X5355 better or the same as:

Intel Core 2 Extreme Quad-Core QX6700, 775, 2.66GHz, 1066MHz FSB, 8MB Cache, Retail

Those are socket 771, which is for servers (i.e. more than one CPU socket), which cannot be used for gaming or overclocking.

There are reports that the 775 Xeons will overclock better than the Core 2 branded CPUs, but it's your call, as not all motherboards support them (like mine *sad face*)