Verdict: The E6750 and E6550 are great value for money.

From the moment we were first able to play with a Core 2 Duo in the spring of 2006 (we weren't allowed to talk about it publicly until the summer), we knew Intel was on to a winner.

Two high-performance cores sharing a large 4MB Level 2 cache combined with the Intel P965 chipset was a match made in heaven. A few of these early models are still available, such as the E6700 and E6600, but Intel has spent the past 18 months fleshing out the series with a whole range of accompanying models.

This means that there are now three distinct flavours of Core 2 Duo, all based on the same Conroe core, so each variation supports 64-bit instructions, SpeedStep, Execute Disable and SSE3. All the models beginning with the characters 'E6' have 4MB of Level 2 cache to share between their two cores, but are further divided between those that end in '50', which have a 1,333MHz effective FSB, and those that end in '00' or '20' and have a 1,066MHz effective FSB. Meanwhile, the models that start with 'E4' have 2MB of shared Level 2 cache and an 800MHz effective FSB.

As Intel launched the E6850, E6750 and E6550 at such a low price, but barely dropped the price of the aging E6700 and E6600, neither of the latter two CPUs are worth buying now, unless you have an older motherboard that doesn't support the 1,333MHz FSB. In fact, the 2.66GHz E6700 is a good deal more expensive than the identically clocked E6750, even though the latter is noticeably faster, thanks to its higher FSB. The E6850 retains its position as the fastest dual-core CPU in the world, but it isn't worth the price. You'd be far better off buying an E6750 and a good HSF, and overclocking it. On the topic of overclocking, all the Core 2 Duos have lots of headroom, most being capable of running at 3GHz or higher with ease. In fact, the higher-spec models such as the E6750 and E6800 can easily be made to run at 3.6GHz, even with a standard low-cost HSF.

AMD's 6400+ Black Edition, which retails for around £14 more, is the nearest in price to the E6750. However, the E6750 was noticeably faster than the 6400+ Black Edition in our Media Benchmarks, Folding@home test and SuperPi. It also gave the AMD CPU a real bruising in games, managing a 50 per cent higher minimum frame rate and 46 per cent higher average frame rate in Supreme Commander. The E6750 is also a lot more power-efficient than the AMD processor - the entire system consumed an environmentally friendly 193W.

The comparison between similarly priced low-end Core 2 Duo and Athlon 64 X2 processors is equally unfavourable towards AMD. For example, the E4600 and Black Edition 5000+ both cost around £80, but the Intel CPU is faster in games and applications, and consumes less power. However, due to their smaller Level 2 cache, E4-series CPUs are slower than the E6-series Core 2 Duos in certain situations, such as simultaneously running multiple applications or gaming.

The only drawback of the Core 2 Duo is that the series stops at around £70, while the Athlon 64 X2 series plunges all the way down to £38. This is great news if you want a low-cost dual-core chip, although Intel has a competitor for these super-cheap CPUs in the form of the Pentium E2100-series.

For most activities, however, an E6-series Core 2 Duo offers the best combination of performance, features, power efficiency and overclockability of any CPU series on the market.

• PSUs - 14th July 2008
• Multi-GPU graphics - 20th June 2008
• CPU water cooling - 17th June 2008
• Hard disks - 20th March 2008
• Audio hardware - 29th February 2008
• Graphics cards - 24th January 2008
• CPUs - 21st December 2007

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