This is Intel's new biggest hitter. It's still the Kentsfield core, but an FSB raised to 1333MHz bumps the clock to 3GHz.
For that hike, you'll need a motherboard supporting a bus of 333MHz or greater, so for now we're talking an Intel P35 or an Nvidia 680i.
The difference is in the overclocking. The crazy nitrogen-cooling contingent have already taken this chip past 5GHz. We reached 3.6GHz (and 690 fps in S.T.A.L.K.E.R) on aircooling with no complaints.
Voltage tweaks and superior coolers should get you close to 4GHz. The secret is the new G0 stepping, which increases frequency potential, reduces power consumption and improves heat dissipation.
It's stupidly expensive but great.