The fastest clocked Core i5 CPU is the 670, clocked at 3.46GHz, but this CPU won’t have the fastest GPU of all 32nm dual-core Westmere-based Clarkdale desktop CPUs.
The runner up, branded as Core i5 661 runs at 3.33GHz CPU speed and with a little help from overclocking it can reach 3.6GHz for one or all cores. Since the TDP of this CPU will be able to reach 87W, its GPU will end up at 900MHz.
This will definitely end up as the fastest clocked IGP, as Intel's G45 express IGP works at 800MHZ for the X4500HD chipset. This can give you an idea that the new IGP, even if its very similar to G45, will still end up slightly faster, but Intel might have changed the IGP in Clarksdale to be more efficient than G45’s.
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PC Hardware
Top Core i5 IGP works at 900 MHz
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Higher 87W TDP