I think sandy bridge will be a blockbuster.
Overclocking as we know it is gone, but the "K" models actually make it simpler. Just raise the multiplier until you hit the thermal wall. That wall will be higher with 32nm chips.
If your app is momentarily not using all cores, the remaining active cores get increased power.
On a clock for clock basis, you will see a 15% improvement.
A good prefiew article from a knowledgeable source:http://www.anandtech.com/show/3871/the-sandy-bridge-preview-three-wins-in-a-row