We learned that the upcoming Core i7 975 is not just a clock-bump from the current top-of-the-line model, the i965. Core i7 975 packs a lot of optimizations under the copper bonnet [IHS], but that is not all.
Intel was the undisputed king of overclocking for almost three years now and AMD changed that with the introduction of Phenom II, clocking it as high as 6.45 GHz on public events. Verified CPU-Z database show the highest clocked quad-core at 7.1 GHz and you've guessed it right, it's Phenom II again. This fact doesn't sit well with enthusiastic engineers at Intel performance labs and their answer is no less than around a thousand speed binned i975 units that Intel will use in various events and sell to selected crowd in order to overtake AMD off the highest spot.
So far, not a single Core-based quad-core processor [with all four active cores] managed to break the 6 GHz barrier, and Intel is hoping that i975 is that "silver bullet". Not long now.