We can't really imagine the type of PC computing enthusiast who could set aside $900 for a six-core Intel Core i7 Gulftown CPU and not be up to spending $100 more the Extreme Edition. But that's the sort of people who would opt for the Core i7-970, the hexacore 3.2GHz chip now on sale for $899.
The chip appeared on Newegg's listings and is available to ship immediately. Paying the extra $100 gets you only an extra 133MHz, but you also get the game Shattered Horizons for free (until the end of the month).
Then again, you could put that $100 towards a faster GPU, and you'd probably be better off.