Unfortunately i won't recommend the Core i7 960.
The ASUS Rampage II Extreme is a kick-ass board and is primarily designed for overclocking so I'm assuming you'll use it for that.
Get yourself a Core i7 920 and either go with liquid cooling or buy a maintenance-free liquid cooler like the 'ALC Domino' or the 'Corsair H50'.
With this combination, you can easily hit 3.8Ghz!
If you overclock all non-extreme i7 900 series, you won't find a robust performance difference.
So why waste $300?
Now what to do with the extra cash?
Well I'll leave that to you.