Conclusion
It was to be expected: an SLI computer with GeForce 6800 Ultra or GT beats everything for performance! The performance reserves of an SLI system are tremendous. Even with an Athlon64 4000+ the cards almost always have to wait on the CPU. Only in a resolution of 1600x1200 pixels with 4x FSAA and 8x anisotropic filtering does an SLI system really have to work hard. These should be the preferred operational conditions for SLI. The game itself also has a large impact on the performance boost afforded by SLI. While shader-intensive games like Doom3 and Farcry benefit from SLI in lower resolutions, the performance improvement with older games like UT 2004 and Call of Duty turns out to be much less. Even Half-Life2 only gets limited benefit from SLI. At present a number of games will not run at all with SLI.
We will only be able to judge how well a GeForce 6600 GT SLI setup performs compared to a single GeForce 6800 GT when new test cards arrive. One thing is already clear however: SLI is by no means inexpensive.
When buying an SLI system you should note that not all games work with this mode. Without the right SLI profile in the driver the game runs only on one card with SLI activated, and sometimes even more slowly than when SLI is deactivated. The game's age and level of 3D technology also play a large role. A further problem is that there are not yet any street prices for GeForce 6800 PCIe cards and the extra cost of an SLI-capable motherboard is not known. Current price talk is around $50 versus a standard nForce 4 Ultra motherboard.
Among the SLI-compatible nForce 4 motherboards we tested our nod goes to the ASUS A8N-SLI Deluxe, not just because of its better performance. Even though MSI will undoubtedly get a handle on the memory bandwidth problems with the final samples of the K8n Diamond, the ASUS motherboard scores points with its two additional x1 PCIe Express slots, which you may search for in vain with MSI. Another factor is that the power supply requirements with ASUS are somewhat less thanks to the additional power connector.
We disapprove of the situation that SLI currently is only possible with games released by NVIDIA. Similar to overclocking, we would like to see an option in the driver allowing you to force SLI operation, even if this involves potential error messages and crashes. Ultimately SLI is only something for the pure enthusiast. Anybody who is willing to invest over $1,000 for 3D graphics on his computer will also be able to live with the risk of an occasional game or computer crash while running SLI. Waiting for the next driver update or using some kind of leaked driver in order to use SLI with a new game is not a lot of fun and will most certainly not be seen as acceptable by the group for which it is targeted.
Other applications for SLI motherboards include a setup using more than two monitors. Those fanatical enough can even install both an ATI and an NVIDIA graphics card into their computers at the same time.
