Xeon or i7

Xeon is the server processor, which is tweaked for server programs. Therefore if you're going for a LGA1366 machine, Core i7 should be more suitable for you.

The cheaper 35xx do not have Hyperthreading and are a complete waste.

The XEON W3520 is an I7-920 but with ECC (error correcting memory bits) on its QPI memory bus. It is a quad core Nehalem with the D0 stepping. It is a single CPU workstation possessor and uses the same X58 chip set as the I7 family.

I have not determined whether the Xeon will work in an I7 mother board. It is possible that the MB makers wired up the 30 additional pins to the memory sockets or that the the Xeon will automatically detect the absence of ECC memory and fall back to operating as an I7-920. Unfortunately I have not found the answers to those questions yet.

The real reason for pursuing this is that the Xeon is more available and cheaper than most people i.e. tank guys are selling the D0 for. That should change when the older C0 stock get depleted and the Neweggs etc have more D0's.

same chip with ECC if you get a D0 I7 920 (they can be C0, or D0 like the xeon)

also, it may or may not have locked memory multi for OCing depending on how your mobo handles it, on my X58 3x sli it handles it no problem according to other users with the xeon.