May as well get the bad news out of the way first. Try as I might, I simply could not get SLI to work properly in any mode with this game. Combine comparatively immature drivers for the technology with this game's major CPU limitations and what you see below is what you get. For this test I used the Primeval timedemo, which demos an intense Onslaught match with several players, vehicles and explosions. I ran the benchmark three times at each setting and took the average frame rate. All in-game settings were put to their maximum, except physics detail, which was set to low to try to lower CPU overhead. Sound also was disabled.
Unreal Tournament 2004 - Primeval Demo
You will notice how I used the split-frame rendering mode to obtain my results. The default profile in the 71.81 drivers is for alternate-frame rendering. I was reading Chris Ray's SLI investigation in the forums. He realized a performance increase in the most GPU-intensive situations in UT 2004 by switching the profile to SFR. Obviously this didn't work for me and in fact had quite the opposite reaction.
Using the default AFR profile made no difference in terms of benchmark scores. The differences were often less than 1 frame per second, even at the highest resolution and image quality settings. I wouldn't say the picture is totally bleak, however. In addition to other game tests showing improvements with SLI, you can use the NvSLI Application Optimizer to force UT 2004 to use single GPU rendering even if you have the SLI checkbox enabled in the driver control panel. Set it, reboot and forget it. Scores jump back up to their normal single GPU levels.
I will spare you the particulars of everything this game has going for it. In spite of a rocky launch, Valve Software has been, in my opinion, pretty responsive to fixes, bugs, and performance issues relating to the single-player aspect of this game. I personally don't play any of the multiplayer aspects, but I continue to enjoy the solo campaign.
In this game, I used the popular benchmarking program Fraps to record game performance in a self-created demo. I chose a nice segment of the "Highway 17" level that features a variety of indoor and outdoor scenery. I spent time calculating the best ways to take my run, and then ran through my own demo three times using Fraps' built-in benchmarking capability. All in-game settings were set to the game defaults, which was high except for the reflection setting, which defaulted to "Reflect world."
Half-Life 2 - Highway 17
Some nice improvements here when you up the resolution from 1024 to 1280 and from 1280 to 1600. I highlighted the 1600x1200 results to illustrate this point. While 4xAA/8xAF remains unplayable, that's more a limitation of the 128 MB of video memory and 128-bit memory interface. Imagine the results were I running a pair of PCI-Express 6800 GT or Ultra cards.
Out of sheer curiosity, I decided to run a quick test on this map at 1280 resolution but dropping the AA and AF to 2x and 4x, respectively, with SLI enabled. Scores from the averaged out runs: 35 min and 82 avg. The 35 happened only for a spilt second and was not to be seen in any other parts of the test. I personally find this setting ideal for my tastes - solid IQ and performance all rolled into one, no doubt thanks to the second video card.
Here's the first game that was engineered to take advantage of the GeForce 6-series support for Shader Model 3.0. While it was through a patch, it was nice to see developer hop on-board with this added feature. Tests of this game used the split-frame rendering mode. As with Half-Life 2, I used Fraps to record a demo. I used a portion of the Training level, again featuring indoor and outdoor environments. All in-game options were set to their highest levels, except for shadows, which were set on medium. Hardware audio was disabled as well as it would cause the game to stutter and slow to a crawl.
Far Cry - Training
SLI also is doing its job in this title, albeit somewhat less effectively than in Half-Life 2. This likely is due, however, to some limitations within the game engine. Not only in this level but also other spots in the game give problems for video cards. My former GeForce 6800 GT would occasionally struggle in some areas, that's why you're seeing a bit more consistency in the low frame rate measures at 1024 and 1280.
Using SLI at 1280x1024 and dropping the anti-aliasing to 2x (low) gave scores of 27 min and 45 avg.