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

Clearly, the times of static and excessive overclocking are over, at least for those of you concerned with how much juice your CPU is sucking down. Although you still get the most performance out of multiple cores that run at maximum speeds, the power level necessary to maintain these high speeds (up to 4.2 GHz in the case of a Core i5-750) is simply unreasonable and unnecessary. We’d much rather have a cool and quiet system that’s kinder on the electricity bill.

It actually makes so much sense to overclock the Core i5 from its 133 MHz base clock to a little more that we recommend this to every user who is interested in getting more risk-free performance at zero cost. Moving from a 133 MHz BCLK  to 150 or 160 MHz, which was the maximum setting in our tests that didn’t require a voltage increase, does not increase your total system idle power. Apparently, the processor power saving features keep idle power in check very efficiently. Peak power, which would be our top reason against high overclocks, still doesn’t explode. We measured less than a 6% increase in peak power on the MSI P55-GD65 when going from a 133 to 160 MHz clock. This had the processor reaching 3.36/3.84 GHz maximum clock speeds in the two applicable Turbo Boost modes (one to two and three to four cores used).

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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.