Overclocking

Our 6800GTs managed to overclock to 385 / 1.08 from the stock 350/1.0 so overclocking is not necessarily hampered by SLI. We only managed to squeeze a few megahertz out of the 3D1 so we are fairly certain that it was a card specific limitation.

Conclusions

SLI is fast and in graphics intensive tasks, it certainly does not seem that NVIDIA is exaggerating about the nearly doubling in performance. In the 3DMark05 features test especially, the theoretical max for fill rate, pixel and vertex shading were very close to a 100% increase on the 6800GT pair. For the most part, games had pretty good framerates even when enabling 8xS antialiasing - this is important for LCD users that are limited with resolution choices. For games that are heavily graphics dependent such as DOOM 3 and Halo, the effectiveness of the second graphics card is very apparent. For older games, the differences are not immediately seen until higher resolutions paired with high AA/AF settings are used. This leads into a design philosophy question - two blockbusters this year, DOOM 3 and Half-Life 2 seem to have taken tangents. id has gone with pushing graphical boundaries while Valve has put more of the emphasis on processor power. If developers continue down the id route, the benefits of SLI at lower resolutions and settings will be more apparent as this is where the performance jump with SLI will be seen. On the other hand, if a game engine is more dependent on the processor side, the power of SLI will be seen at the higher resolution coupled with high AA/AF settings.

On the upgrade side, SLI provides some interesting options for the end user - they will have a choice to simply add a second card to increase performance at some time in the future or the traditional route of upgrading to a more powerful video card. The former is pretty compelling as prices tend to drop and adding a second card should be less cost prohibitive than paying for something that is outright more powerful. Something to note however is that the same dataset is loaded onto both cards which means the total amount of memory available is not a simple addition of the onboard memory size. This is something that may be more relevant as we have seen in DOOM 3, the amount of memory available directly affects the texture quality setting that can be used comfortably.

The entry fee to the SLI party will be what the end user puts into it. For those that have hit their blood and/or other body fluid selling quota for the month, a 6600GT and a SLI board is not a huge additional investment over a nForce 4 Ultra board. With several manufacturers set to introduce nForce 4 Ultra based boards capable of SLI including DFI, the price gap should continue to shrink between SLI and non-SLI capable boards. This does not imply that SLI for hardcore users will be cheap - a pair of 6800GTs or 6800 Ultras will go for roughly 800-1000$ though that is not too different from shelling out for the latest Athlon FX. We also suggest that end users who are interested in a pair of 6800GTs or higher to get an appropriately fast processor as the bottleneck will not be the video card in the majority of cases.

Like with the rest of the GeForce 6 family, NVIDIA has done an impressive job with SLI and is just riding more than just hype - they have the goods to back it up and literally bring next generation performance to the desktop today. In the span of roughly 8 months NVIDIA has managed to more than quadruple processing power in their GPU lineup. It almost puts the damper on next generation parts, but hey, they can be SLIed too. It is going to be a good year on the hardware side.