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Efficiency Explored: What's The Perfect Clock Rate For Your Core i5?

Efficiency Explored: What's The Perfect Clock Rate For Your Core i5?

3 GHz? 4 GHz? Not a problem! Pretty much all Core i5 and Core i7 models are capable of running at overclocked speeds, delivering stellar performance. You only need a suitable platform to sustain your overclocking ambitions. However, even such an efficient product as the Core i5/i7 will no longer be energy-friendly if clock speeds are tweaked to the extreme. We looked at the Core i5-750 and overclocked it (with Turbo Boost enabled, per your requests) to find the clock speed that delivers the most optimized performance per watt.

How Much Overclocking is Good?

Efficiency and power consumption have become an integral part of evaluation the latest CPUs, in addition to the performance, value-added features, and cost already commonly discussed. Preserving natural resources worldwide is a hot topic for debate, of course, and we’d never encourage anyone to burn energy unnecessarily. But when we’re talking about PC hardware, one has to moderate being eco-friendly with getting stuff done. This is not about trying to save the world. This is about maximizing system value with a focus on sense and reason.

Some years ago, when overclocking wasn’t as popular and widespread as it is today, enthusiasts mainly wanted to maximize performance. This was a logical step. Faster systems—and processors in particular—were highly desired, whereas even today’s entry-level PCs have sufficient horsepower for pretty much all mainstream PC applications (a handful of games excepted). Expense wasn’t measured at the outlet like it is today. Rather, heat dissipation was the major issue once the platform was capable of decent overclocking.

In the first half of this decade, AMD and Intel both cranked up the heat with their processors, moving thermal limits from roughly 30W in the Pentium III days to a maximum of more than 130W. Certain chips, such as the fastest Pentium 4 CPUs, were even forced to throttle clock speeds when they hit their thermal limits. This is when we first started to wonder whether an additional 20% clock speed at the price of almost doubled power consumption made sense.

Hunting Down the Sweet Spot

We’ve already looked for the best ratio between overclocking, performance, and power consumption in an effort to find the most efficient operating parameters for Core 2 Duo, Core i7, and Phenom II X4. For more on those stories, check out:

Overclocking Core 2 Duo: Power Vs. Performance

Overclocking Core i7: Power Vs. Performance

Optimizing Your Phenom II Overclock For Efficiency

Now it’s time to do the same with Intel’s Lynnfield-based entry-level model, the Core i5-750, which we consider one of the best and most reasonable choices for mainstream users with performance ambitions.

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  • 1 Hide
    mi1ez , 12 January 2010 14:31
    Fantastic and highly anticipated article. I think this has just about convinced me to go i5 and OC with turbo enabled. Would be interesting to see a few gaming benchmarks too and perhaps the temperature charts. I'm just as interested in keeping temperatures down as I am power consumption.

    Cheers Tom's, Really informative article.
  • 1 Hide
    b82 , 13 January 2010 05:13
    Brilliant. I'd already decided to buy an i5-750 and had been wondering about a moderate overclock of up to about 20%, with turbo on. Aside from consideration of not overstressing the processor, maintaining reasonable efficiency was something I did have in mind. I was worried that any decent overclock would damage efficiency.

    I didn't imagine that anyone would produce such a detailed anaylsis, and even an attempt at an efficiency curve. The answers I wanted (more even) on a plate.

    Excellent, and for me very timely.
  • 1 Hide
    Anonymous , 13 January 2010 21:54
    The one thing I love about my i5-750 system is I have pretty good performance but a whisper quiet case. I assume to overclock to these levels I'd need a pretty decent (ie LOUD) cooler?
  • 0 Hide
    b82 , 14 January 2010 01:36
    joyorkI assume to overclock to these levels I'd need a pretty decent (ie LOUD) cooler?
    Um, they tested at a variety of overclocks, so not sure which levels you mean by 'these levels'.
    However, I think you would do well to check out Noctua fans and coolers. They are not cheap, but they are high performance (taking noise into account). If you check out this table here:

    as an example, you'll see that Noctua's airflow per decibel on their fans is very high. They make a few models of expensiv(ish) but well rated coolers.

    Edit: The Scythe S-Flex range also looks good on airflow per decibel.
  • 1 Hide
    G-M , 14 January 2010 16:30
    Very nice article, I have my i5 at 3.2 currently as it is the highest BCLK that doesn't require a voltage change. At 160 it has the benefit of allowing my RAM to run at native 1600, though that is probably of marginal importance.

    For cooling I would highly recommend the Hyper 212, with the settings mentioned above I idle at ~25C and peak with prime95 at 58C, all at very low fan RPM and noise.
  • 0 Hide
    freedonian , 14 January 2010 23:29
    What CPU cooler is being used in the test setup?
  • 0 Hide
    kramcd , 20 January 2010 03:06
    Exactly the type of info I wish to know. Could you please, please do a similar article for the i7-860 CPU?
  • 0 Hide
    i5-750ish , 6 April 2010 14:05
    The cooler is the MUX-120 from Thermalright. That was the 'overclocking' cooler Intel sent to reviewers for the 1156 roll out. It's mentioned in the 1156 cooler review at:,2535-8.html

    The interesting question is why the fan is mounted to pull, not push. But, perhaps that mounting position was selected by the 'art' director during the glamorous photo shoot.

    It was that Tom's 1156 cooler review that pushed me towards the Mugen 2 - which is a mounting nightmare. Kinda wish I'd purchased the svelte MUX-120. And may yet when the 800 lb. Mugen gorilla shreds the MB when it comes time to put in the case.