Intel Core i5-655K & Core i7-875K review

Technically, Intel’s new Core i5-655K and i7-875K CPUs are a very minor tweak to the existing i5-650 and i7-870 parts. They have the same number of Hyper-Threaded cores (two and four respectively), the same cache configurations and the same basic clock speeds – 3.2GHz for the Core i5 part and 2.93GHz for the i7.

The difference is, these new models are designed to be overclocked. Though the basic frequency multiplier is locked, you can freely adjust the “Turbo Mode” multipliers that kick in when the CPU is under load. It’s a smart way to get the best from these chips: there’s no sense in pumping up the power (and the heat) until there’s work to be done.

Benchmark scores

We tested the new chips in an Intel DP55WG motherboard with 2GB of DDR3-1066 and an ATI Radeon HD 4550 graphics card. The 32nm i5-655K comes with Intel’s integrated HD Graphics GPU, but the i7-875K, based on the older 45nm Nehalem architecture, lacks an onboard GPU of its own.

Out of the box, the i5-655K achieved an overall benchmark score of 1.86, while the i7-875K hit 1.93. These scores are surprisingly different to those we’ve seen before from the vanilla 650 and 870: presumably Intel has tweaked the power envelopes that determine when each processor goes into Turbo Mode. Happily, this is user-adjustable, so if you wish you can make the CPU leap to Turbo frequencies at the drop of a hat.

And when it comes to overclocking, both chips leave their elder siblings in the dust. With a stock Intel heatsink and fan we were able to turn the Turbo Boost multipliers up by a massive five ticks before the system became unstable. This let the i5-655K blaze through our benchmarks at speeds up to 4.1GHz for an overall score of 2.16, while the i7-875K hit 4.3GHz and scored a magnificent 2.31. With a custom heatsink it will probably go even faster.

Specialist appeal

Although Turbo Mode is designed to be self-managing, we had to engage in extensive trial and error to achieve these optimal scores. That’s likely to discourage the typical home user.

And the price isn’t exactly cheap: on a strict bang per buck calculation you’ll get better value from any of the regular Core i5s, even if you overclock the new models. And AMD’s quad-core Phenom II chips beat anything Intel has to offer. (Click chart to enlarge)

But there’s always a premium to be paid for aspirational performance, and when you look at the price of a Core i7-900 processor, these new models look like a stunning bargain. If you’ve chosen the LGA 1156 platform, and you’re willing to get your hands a little dirty in the name of performance, the Core i5-655K might be Intel’s best deal ever, with the Core i7-875K a premium cherry on the cake.