Lynnfield CPUs overclock in a very similar way to LGA1366 Core i7s. The only significant difference is overclocking the Base Clock with Lynnfield compared with the QPI of LGA1366 Bloomfield CPUs. As the QPI frequency is equal to the Base Clock frequency, the terms can be used interchangeably, but you're unlikely to see the term 'QPI' in the BIOS of a P55 motherboard. You'll still find 'QPI Link', which is the bus between the CPU and memory, and is derived from the Base Clock and a multiplier (the memory strap).
With Turbo Boost (rev 2) disabled (it gets confused by overclocking), we successfully boosted the i5-750 from 2.66GHz to 4.2GHz by setting a CPU multiplier of 22, a Base Clock of 191MHz, a vcore of 1.425V, an IMC voltage of 1.3V and setting the CPU PLL to 1.9V. This overclock boosted the overall Media Benchmarks score from 1,474 to 1,953 and added another five to 11fps to gaming performance.
The i7-860 didn't overclock quite as well, going from 2.8GHz to 4.09GHz with a CPU multiplier of 22, a Base Clock of 186MHz, a vcore of 1.375V, an IMC voltage of 1.3V and a CPU PLL of 1.9V. This overclock increased the overall Media Benchmarks score from 1,621 to 2,070 - the Hyper-Threading of the i7-860 helped it to beat the i5-750 despite its lower overclocked frequency.
In contrast, the i7-870 proved to be a woeful overclocker. Despite being the same CPU as the i7-860, the i7-870 overheated and throttled its frequency to around 3.5GHz every time we tried to overclock it close to 4GHz. As a result, even after testing three replacement CPUs from various sources, and five different coolers, we had to settle for a final overclock of 3.78GHz. This required a CPU multiplier of 22, a Base Clock of 172MHz, a vcore of 1.275V, an IMC voltage of 1.275V and a CPU PLL of 1.9V. As a result, the manually overclocked Core i7-870 didn't perform significantly faster than when the chip was running at default speeds with Turbo Boost (rev 2) enabled.
While the overclocked Lynnfield CPUs leave the overclocked Core 2 and Phenom II CPUs way behind, the i7-920 comes into its own when overclocked. With an overclocked frequency of 4.08GHz (with a 20x multiplier with a 204MHz QPI), we saw epic scores from this £205
CPU: its overall Media Benchmark score of 2,241 is eight per cent faster than the fastest Lynnfield score.
WPrimeDownload from: www.wprime.net
WPrime is a multi-threaded maths calculation benchmark that counter-intuitively uses square roots rather than prime numbers. The standard benchmark uses 32 million numbers, calculating the square root via 'a recursive call of Newton's method for estimating functions'. We're not sure what that means either, but you can read the full blurb on WPrime's About page
. What we do know is that WPrime scales well across multiple CPU cores, and can push a CPU to 100 per cent load on all its cores.
To run the benchmark, first visit the core count to check that WPrime will load all physical and logical cores, and then run the 32M test. The results are expressed as a time taken to calculate the square root of the set of numbers (32 million in the standard test). A lower score is better.
Intel Core i7-870
Intel Core i7-920
Intel Core i7-860
AMD Phenom II X4 965 Black Edition
AMD Phenom II X4 955 Black Edition
Intel Core i5-750
Intel Core 2 Quad Q9650
Intel Core 2 Quad Q6600
Intel Core 2 Duo E8600
seconds (lower is better)
For analysis of these results, please read the Results Analysis