Overclocking the duo
875KThe Intel Core i7 875K is, as we've said, practically identical to the 870 model that ships in reasonably high-end desktops.
Idling at 1.2GHz and Turbo Boosting up to 3.6GHz when a single core is used, the fun starts once you add a little voltage.
Cooled by a Thermalright Ultra Extreme and 120mm fan, we increased the Vcore from 1.175V to 1.325V and then increased the mulitplier until failure. The chip was rock-solid stable with a 31x multiplier (4135MHz) but exhibited the odd stability problem at 32x (4,258MHz). Under-load temperature hit 74°C, according to the motherboard's PCProbe software, and the overclocking headroom may well be compromised by heat-related issues as much as the frequency ceiling.
655K
Much like the 875K, the 655K does a perfect job of replicating a Core i5 650 chip when put straight into a motherboard, running at 3.2GHz and Turbo Boosting up to 3.46GHz.
Give
it some love by increasing the
voltage to 1.32V, resulting in an under-load temperature of
59°C,
and the chip nears 4.5GHz.
A
little unstable with a 34x multiplier
(4,549MHz), a 1.2GHz overclock over default frequencies is decent for
the
dual-core, quad-threaded chip. Expect more if you put some really
heavy-duty cooling on it.