Verdict: Not worth it in SLI.

The 320MB GeForce 8800 GTS is one of the oldest cards in this Labs test, and is quite hard to buy now. However, it was very popular in early to mid 2007 thanks to its excellent price-to-performance ratio, so we thought it important to discover whether it's worth buying a second card for SLI or ditching your 320MB 8800 GTS and getting a whole new card altogether.

The 320MB 8800 GTS, like the 640MB 8800 GTS and 8800 GTX before it, is based on the G80 architecture. Its 96 stream processors are clocked significantly higher than the rest of the GPU (1.2GHz versus 500MHz), but to keep costs down, the card has only 320MB of comparatively slow RAM running at 800MHz (1.6GHz effective) via a 320-bit memory controller.

Unfortunately, time hasn't been kind to the 320MB 8800 GTS. A year ago, this cut-price card could cope with most games at 1,680 x 1,050, but it produced a smooth minimum frame rate in just three of our ten test games - Oblivion, Need for Speed: Pro Street and Team Fortress 2. Call of Duty 4 had a minimum frame rate of 23fps, which could be easily bumped above 25fps with a little overclocking, but you can forget about playing ArmA and Crysis without massacring the detail settings on the 320MB 8800 GTS - both games had minimum frame rates below 10fps, making accurate shooting impossible.

The 320MB 8800 GTS's poor performance is no doubt due to the increased complexity of modern games, so the card's comparatively small 320MB frame buffer is simply too small to store everything needed. The 320MB 8800 GTS also wastes a lot of power: our system drew 335W with the card maxed out, which is just 10W less than the far faster G92 based 512MB 8800 GTS.

Two-card SLI

If you've found that your 320MB 8800 GTS is struggling to play the latest games smoothly, you may have considered buying a second card for SLI. The game that benefited most from SLI was DiRT. The second 320MB 8800 GTS nearly doubled the minimum frame rate, boosting it from 21fps to 41fps. If every game responded as well to a second GPU, we'd be much more enthusiastic about SLI and CrossFire, but unfortunately, this isn't the case. For example, the minimum frame rate in S.T.A.L.K.E.R. barely moved at all, improving (although that's really too strong a word) by a minuscule 1fps. However, far worse was to come.

After spending £80 upgrading your PC and adding 124W to its power draw, in our experience you can look forward to the frustration of Crysis crashing when you try to load a level with a pair of 320MB 8800 GTS running together in SLI.

We succeed in coaxing ArmA and Oblivion to run, but both games slowed down with SLI enabled. The minimum frame rate in ArmA dropped from an already painful 9fps with a single card to an abysmal 6fps in SLI. In our two RTS test games, the results were mixed. In Supreme Commander, SLI helped the average frame rate increase by 44 per cent at 1,680 x 1,050 and 58 per cent at 1,920 x 1,200. Unfortunately, the minimum frame rate fell in both cases, and in Company of Heroes, both the average and minimum frame rates were ground down by the extra card. Arguably, a high minimum frame rate isn't as crucial in an RTS as it is in an FPS or driving game, but a decline from 8fps to 5fps in the latter at 1,680 x 1,050 when we added a second card is a very poor return.

Conclusion

According to Nvidia, one of the biggest selling points of its graphics cards and motherboards is that when you need to upgrade, you can add a second graphics card in SLI and boost the performance of your PC. However, our test results show that adding a second 320MB 8800 GTS to your PC is one of the worst upgrades you can make. Highlights were depressingly few and far between. Team Fortress 2's minimum and average frame rates improved dramatically with a second card, but it already runs so fast on a single 320MB 8800 GTS (with a minimum of 44fps, even at 1,920 x 1,200) that an upgrade is unnecessary. Both driving games were improved by SLI, as was Supreme Commander, although there are caveats. DiRT became faster only at 1,680 x 1,050, and in Supreme Commander, only the average frame rates improved - having two cards couldn't lift the game's minimum frame rate, and in fact made it worse.

In our other test games, SLI provided relatively small performance gains, such as a 7 per cent faster minimum frame rate in S.T.A.L.K.E.R. and 22 per cent in Call of Duty 4. In general, the benefits were only apparent at 1,680 x 1,050 too - an extra card couldn't make many games playable at 1,920 x 1,200 if they weren't already playable with a single card. In other titles, SLI actually degraded performance. The frame rate in Oblivion and Company of Heroes took a modest hit while ArmA's suffered a huge setback, and of course, SLI stopped Crysis dead in its tracks. It certainly didn't help that Nvidia hadn't bothered updating its WHQL drivers for the 320MB 8800 GTS in nearly five months. However, there's no excuse for charging consumers an extra £80 for a second graphics card that makes their PCs hotter, noisier and in some cases, less stable, while doing so little for performance. Our advice if you still own a 320MB 8800 GTS and are getting frustrated by its poor performance in modern games is to sell it on eBay and buy a faster single-GPU card, bypassing SLI altogether.

• 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

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• 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