Intel's Nehalem CPU architecture is a scorcher in quad and six-core trim and it makes for an impressive in dual-core chip, too. Running at the standard 3.2GHz clock (add a few hundred more MHz when Turbo Boost kicks in), the dual-core Intel Core i5 665K is a match for quad-core processors such as the AMD Athlon II X4 620.
For that you can thank HyperThreading, which allows the Core i5 665K to simulate the presence of an extra pair of cores. What's more, you get an integrated graphics core built into the CPU itself (note, however, that not all LGA1,156 motherboards will support the graphics functions).
But none of this is enough to match more powerful AMD quad-core processors such as the Phenom II X4 965 BE or Intel's own Core i5 760, all of which are actually cheaper and hammer the Core i5 655K in literally all of our benchmarks.
Incredibly, the six-core AMD Phenom II X6 1055T can also be had for about £10 less. That's a chip that hoses the Core i5 655K even more comprehensively. The 655K has a tough time justifying its existence.
All of which leaves us wondering whether the 655K's unlocked processor multiplier can make the difference. The simple answer is no. In our testing, the Core i5 655K actually overclocks better via the baseclock, not the multiplier. Still, overclock well it does, hitting 4.2GHz with a little help from some extra voltage.
Unfortunately, Intel's similarly priced quad-core processors will also nail 4GHz or higher, leaving 655K back where it started - bringing up the rear.
If dual-core computing was state of the art, this chip would be our weapon of choice. Thanks to HyperThreading, Turbo boost and the awesome Nehalem architecture, it's a seriously quick dual-core processor. It also runs cool, uses little power and overclocks well.
Unfortunately, dual-core computing hasn't been cutting edge since 2006. The Core i5 655K therefore costs too much and delivers too little processor performance compared to similarly priced quad and six-core alternatives. As for the built-in graphics core, it's no good for gaming.
Intel makes some outrageously good CPUs. This isn't one of them. It's the wrong chip at the wrong price.
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