I'm planning on buying a new processor/motherboard soon, and wondered why there was such a huge price difference between the regular i7 and the Extreme Editionhttp://www.buzzle.com/articles/symptoms-of-ovarian-cysts-bursting.html .
One of the main difference is that the system bus speed is higher for the Extreme Edition.
Usually Extreme CPU are for high-end users like gamers, graphics media etc, intensive simulation.
Before getting a new system, make sure to check the cpu compatibility with the board as there are two types of i7, one with socket 1366 and other one with 1156. They are not pin compatible.
All the best,