Benchmarking with Doom 3 can be very tricky. The game itself is limited to rendering only 60 fps by the game engine. This limit is removed however when running the benchmarking modes. This can make things a bit tricky for the benchmark results. The goal is to find a setting with the highest graphics that will still have just above the 60 frames per second for the best graphical experience.
The benchmark tests were conducted using the demo001 included with the retail release of the game using the Doom 3 console commands. All benchmarks were conducted with the high quality graphics settings and run multiple times to properly cache the graphics data. Auto overclocking modes were not included in the results because the game failed to render properly with it enabled.
The SLI mode from NVIDIA definitely shows a strong performance gain for Doom 3. In fact, it showed roughly a 80% performance gain at the 4x AA, 8xAF graphics settings. This enables the game to run at a high quality graphics mode and still be very playable while the non-SLI is starting to drop towards the acceptable but noticeable frame rates.
The single 6800 GT graphics card still performs extremely strong in the game allowing for the 2x AA 8x AF graphics settings with the frame rates above 60. Overclocking did give a roughly equivalent boost in frame rates to the percentage boost in the GPU clock.
