The processor is set to debut in just a few weeks, during September 2010. From what we managed to learn, the i7-990X is based on a new stepping of Intel's 32nm Gulftown core consisted out of six cores and additional six threads. The clock is upped from 3.33GHz to 3.46GHz, while the Turbo mode ticking at 3.6GHz. According to preliminary results we have received, you should have no problems in clocking this processor past 4.5GHz on air, and 5GHz on water should be granted.
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New Intel Core i7 990X Extreme coming in September - Bright Side Of News*
3.6ghz stock clocks with turbo enabled. BUT what is most interesting is the fact that it will be a new stepping, and that usually means lower vcore, temps, and generally OC's better than older steppings.