If you want to run a pair of Nvidia graphics cards in SLI mode then you need a motherboard with an Nvidia chipset. Given that a motherboard with an nForce 650i SLI costs about £70-£75, you might wonder what you stand to gain by spending more than double that price for Nvidia's top-of-the-line nForce 680i SLI.

Happily we're in a fine position to answer the question, as the EVGA nForce 680i SLI is a pure Nvidia reference design that supports Intel's Core 2 Duo.

The most obvious difference is the PCI Express support. 650i SLI has 20 PCI-E lanes in total, with 16 lanes fed to one graphics card or eight lanes each if you have two cards in SLI mode. 680i SLI, on the other hand, has up to 44 lanes, so that's 16 lanes for each graphics cards in SLI plus another eight for the third long PCI-E slot which could accommodate a third graphics card to handle physics calculations, provided that feature is supported by your new game, and there are still a few lanes left over for more expansion slots.

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The second strength of 680i SLI is its support for overclocking, which is handled by nVidia's nTune utility.

Added to that you get a long list of features, just as you would expect from a motherboard at this price, so there are six USB 2.0 ports on the I/O panel plus four more on a bracket, or you can connect the headers to any ports that might be mounted on your case. It's a similar story with Firewire, as there's one port on the I/O panel plus a second on another bracket.

The HD audio has six mini jack connections as well as optical output and there are six SATA 2 connectors with support for RAID 0, 1, 5 and 10. The four memory slots are dual channel, of course, and can accommodate up to 8GB of 800MHz memory. There are two PCI slots and two PCI-E x1 slots ready to accept your expansion cards.

That's a decent list of features, but then you get to the clever Nvidia tricks such as SLI memory which will overclock suitable memory up to 1,200MHz, and the way that the dual Gigabit Ethernet ports can team up to supply a connection that is even faster than Gigabit. We are told that 680i SLI supports a 1,333MHz FSB, however we doubt that it will support the next generation Intel Penryn processor.

And then we start to question some of the features. Take that graphics support, for instance. Dual PCI-E x16 sounds better than dual x8 but in practice there is no real benefit from the extra PCI-E lanes, and if you install two double-slot graphics cards then most of the expansion slots vanish from sight. The six SATA ports also sound impressive compared to the four ports you get with 650i SLI, but honestly, do you want five or six hard drives in your PC?

The final big question mark hangs over the overclocking and specifically over nTune 5. The BIOS for the EVGA allows you to change every setting you can possibly imagine, including all of the buses, all of the voltages and the memory timings. It's a formidable sight, but the whole purpose of nTune is to save you the hassle and to do the job for you, provided your motherboard uses either the 680i SLI or 680i SLI LT chipset.

It looks like a great piece of software, but it does something very odd, as the first part of the overclocking is to crank up the speed of the PCI-E bus from the stock speed of 2,500MHz to just shy of 4,000MHz. This brought no obvious increase in performance yet it meant that the processor would barely overclock at all.

We have little doubt that the EVGA would be a speed demon if only nTune overclocked the buses in a difference sequence, but as things stand the software is useless which means you are paying a huge premium for a chipset that effectively offers very little over the far cheaper 650i SLI.

On paper the 680i SLI looks like a superb chipset but in practice it just doesn't add up. The long list of features is unlikely to be much use to even the most avid gamer, but the real problem is Nvidia's nTune overclocking utility. This piece of software is carrying out a series of sophisticated tasks in the wrong order and as a result it is quite worthless.