Verdict: Not really worth buying in a single-, dual- or triple-card configuration.

The 9800 GTX is based on the same G92 architecture as the 512MB 8800 GTS. Both cards even have the same amount of memory and a 256-bit memory interface, so it's misleading for Nvidia to use the 9-series moniker for the 512MB 8800 GTS. Even under the heatsink it's hard to see any significant differences between the 9800 GTX and 512MB 8800 GTS. The newer card's 128 stream processors run at 1.688GHz compared to the older card's 1.625GHz, while its GPU is 25MHz faster, at 675MHz as opposed to 650MHz. However, the 9800 GTX's 512MB of memory is significantly faster than that of the older card, at 1.1GHz (2.2GHz effective) as opposed to 970MHz (1.94GHz effective), providing a lot more memory bandwidth. The 9800 GTX is cooled by a large dual-slot HSF and powered by two 6-pin PCI-E power sockets.

A single 9800 GTX was able to play most of our test games smoothly at 1,680 x 1,050, with Crysis the noticeable exception. However, the cheaper 512MB 8800 GTS delivered very similar frame rates in most games (although it scaled very poorly in SLI), while two GeForce 9600 GTs in SLI are far quicker but cost a similar amount.

Two-card SLI

Adding a second 9800 GTX boosted the minimum frame rate in Crysis by a significant 41 per cent from 17fps to 24fps. However, a single 9800 GX2 is faster and £50 cheaper than a pair of 9800 GTXs. Still, with two GeForce 9800 GTXs, the other FPS games we used (bar Oblivion) ran significantly faster than with a single card, allowing us, for example, to increase the resolution in ArmA to 1,920 x 1,200 while maintaining a smooth 29fps minimum. DiRT and Need for Speed: Pro Street also liked the extra graphics card, but the minimum frame rates in Supreme Commander and Company of Heroes: Opposing Fronts fell. The minimum frame rate in the latter game tumbled from 37fps to 24fps at 1,920 x 1,200 with SLI enabled.

Three-card SLI

Despite having four 16x PCI-E slots and two nForce 100 chips, the D5400XS Skulltrail motherboard we used to test the other multi-GPU systems doesn't support 3-way SLI. We had to test it with an Asus Striker II Extreme board, which is based on Nvidia's own nForce 790i Ultra SLI chipset. To ensure that the results between the two systems were comparable, we also retested two-card SLI and a single card on the Striker II Extreme, and found that most games ran between 3fps and 8fps faster, a disappointing result for the Skulltrail system and its slower FBDIMM memory. Aside from the 3-way SLI scores, the results on p84 onwards all come from the Skulltrail system, so bear this in mind.

Even with the advantage of running in the faster system, 3-way SLI failed to uphold Nvidia's claims of 'incomparable graphics performance'. At 1,920 x 1,200, the minimum frame rate was slower or no different in most of our ten test games than with two cards running in SLI in the slower Skulltrail PC. For example, while Crysis benefited from the third card at 1,680 x 1,050, raising the minimum frame rate to 32fps from the two-card configuration's 24fps, the game ran slower at 1,920 x 1,200 with the third card. What's worse, the minimum frame rate in DiRT collapsed from a silky-smooth 61fps on two cards to less than 1fps on three cards, even in the game's menu screens. The minimum frame rate in Company of Heroes: Opposing Fronts also took a small hit with all three cards installed. Where 3-way SLI does provide extra pace over two-card SLI is in situations where two cards are already fast enough - Call of Duty 4's minimum frame rate goes from 48fps to 72fps at 1,920 x 1,200, which is a big hike, but 48fps is hardly sluggish.

Not only does 3-way SLI provide little in the way of extra worthwhile performance, it's also very problematic. For starters, you have to make sure all three graphics cards have exactly the same BIOS, otherwise the system may not POST, or may appear to work but use only one or two of the cards without warning you this is the case. Our test system refused to boot at least 30 per cent of the time, and suffered a significant number of crashes. The final nail in the coffin for 3-way SLI is that the three dual-slot cards take up so much space that there's no room for other expansion cards, such as a sound card or Killer NIC - both must-haves for any ultimate gaming PC.

Conclusion

While a single 9800 GTX is undoubtedly fast, buying one for £200 or so makes little sense when the £40-cheaper 512MB 8800 GTS runs most games at similar frame rates, and two GeForce 9600 GTs in SLI provide more power for only a little extra cash. As with two 9600 GTs, two 9800 GTXs make some games run significantly faster, but it's hard to justify the £400 cost and 503W power draw over a £350, 452W GeForce 9800 GX2, which is cheaper, more efficient and plays games smoothly at the same settings and resolutions. This just leaves 3-way SLI, which is a huge disappointment, and far more frustrating than two-card SLI. As with CrossFire, adding more than two Nvidia GPUs brings diminishing returns: the sacrifices you make in price, cooling, power consumption, noise, stability and space for other components is in no way justified by the experience of 3-way SLI.

• Cases - 21st November 2008
• Motherboards - 24th October 2008
• Gaming Headsets - 26th September 2008
• Dream PCs - 24th September 2008
• Headphones - 12th September 2008
• Media PC components - 22nd August 2008
• PSUs - 14th July 2008

• Intel DG45FC - Motherboards
• Intel X25-M Mainstream SATA SSD - Hard disks / storage
• OCZ Core Series 30GB - Hard disks / storage
• Western Digital Caviar Black 1TB - Hard disks / storage
• Asus EAH4870 TOP - Graphics cards
• Creative Sound Blaster X-Fi Titanium Fatal1ty Pro - Sound cards
• Multiwinia - Games