Hey genius, the Core i7 is a quad core too ;p
Technically those two are the exact same thing. The Xeon is a server processor, which makes it better suited for heavy loads, and the i7 EE is a desktop processor, better for quickly loading less apps.
You probably wont notice a huge difference between them, but if you're building a desktop then go with the i7 920, a 965 Extreme is really expensive and not worth it just for the unlocked multiplier.