Intel's Core i7 920, Nehalem microarchitecture derived, 2.66 GHz offering will apparently easily overclock to 4 GHz with air cooling, according to this article from Fudzilla.

We've been hearing a great deal about Nehalem's overclocking potential recently, yet sources are now indicating that whilst overclocking potential will be there, a good motherboard solution will, of course, be required to take advantage of that same untapped potential.

As expected, the Core i7 965 Extreme Edition will likely take the top spot, yet these early reports are an impressive indicator of what we can expect from Intel's Core 2 successor.