Intel’s Core i5-655K & Core i7-875K: Overclocked and Analyzed

When it comes to Intel processors, the word “unlocked” is not synonymous with low-priced mainstream products - it’s a feature normally reserved for flagship ‘Extreme Edition’ CPUs that bear higher price tags. Things are set to change today because Intel is launching the “unlocked” K series of processors to fit into the existing Lynnfield and Clarkdale line-up:

Processor	Core (GHz)	Unlocked	Turbo Frequency (GHz)	Max Mem Clock	Cores / Threads	L3 Cache	TDP	Price
Intel Core i7-980X	3.33	Cores, DDR3, Power	Up to 3.60	3 Channels 1333MHz	6 / 12	12MB	130W	$999
Intel Core i7-870	2.93	DDR3, Power	Up to 3.60	2 Channels 1333MHz	4 / 8	8MB	95W	$562
Intel Core i7-875K	2.93	Cores, DDR3, Power	Up to 3.60	2 Channels 1333MHz	4 / 8	8MB	95W	$342
Intel Core i5-655K	3.20	Cores, DDR3, Power	Up to 3.46	2 Channels 1333MHz	2 / 4	4MB	73W	$216
Intel Core i5-650	3.20	DDR3	Up to 3.46	2 Channels 1333MHz	2 / 4	4MB	73W	$176
Intel Core i3-540	3.06	DDR3	N/A	2 Channels 1333MHz	2 / 4	4MB	73W	$133
Intel Core i3-530	2.93	DDR3	N/A	2 Channels 1333MHz	2 / 4	4MB	73W	$113

While it is interesting that Intel is offering unlocked core multipliers on Lynnfield and Clarkdale, it’s more interesting that the models being introduced are not the most expensive in their respective families. Especially considering that the i7-875K’s stock speeds are identical to the i7-870 while costing less. At $349, it's only a stone's throw away from AMD's 1090T, while you've got the i7-860 coming in cheaper than both. All of these processors can be compared to one another in Bench here and here.
Overclockers will sit up and take note at the prospects of increased flexibility and the potential of alleviating bottlenecks caused by insufficient bus margins on cheaper processors. We've all had CPUs that seem to have additonal headroom for frequency scaling, but are held back because the highest available core multiplier ratio is too low.  We increase reference clock freqeuncies, only to find that some of the related busses aren't completely stable and as a result no choice but to fall back or relax key performance registers which defeats the purpose of performance related overclocking. That's one of the areas where the K-series might help. Another key factor that makes unlocked processors attractive is that they open the doors to easy overclocking for users that like to keep things simple. With unlocked multipliers we can overclock the CPU without having to fiddle around with memory ratios or memory timings, leaving those settings static.

As there are no under-hood changes to the substrates themselves, there’s not a whole lot of benchmarking for us to do in this review. We’ve already compared the performance of similarly clocked non K-series Lynnfield and Clarkdale processors in our platform launch articles and also have a range of comaprisons in Anandtech Bench. Our focus in this write-up is to look at how the i5-655K and i7-875K fit from an overclocking perspective against both their cheaper and more expensive counterparts.
Be for-warned that this isn’t a typical launch piece; it’s full of talk about voltages and harps on about overclocking in a way that will send many readers to sleep. If that isn’t a big enough deterrent, then read on…