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In SLI mode, we encountered two issues with the GeForce GTX 260. First, the fan on the card proved insufficient for the load test, and second, the CPU processing power of the test system was not enough to always properly drive the configuration.
With regard to CPU performance, one argument in favor of a more powerful processor is that anyone who invests in two GTX cards will have the cash available to buy the fastest quad-core chip. While you are not going to get much more graphics performance with a quad-core CPU running below 3 GHz, there are still games that react better to CPU clock speeds versus the number of processing cores. With a pair of GTX cards, you have three options: the game is optimized for quad-core chips and the four cores do their work on a quartet of threads, you buy a dual-core chip that emphasizes frequency for its performance gains, or you wait for a more powerful generation of processors.
MSI’s overclock yields a total benefit of just 2.2% with the GTX 260 running in SLI, while the single-card setup boosts performance by 4.5%. In the individual evaluation at various resolutions, SLI is only perceptibly faster at 1680x1050 pixels with anti-aliasing enabled and at 1920x1200 pixels. SLI becomes more interesting in Assassin’s Creed and World in Conflict at higher resolutions with anti-aliasing. In Call of Duty 4 and Mass Effect the values are considerably better as well. Crysis shows the best increase running at Very High Quality settings with AA. In Quake Wars, Half Life 2: Episode 2, and FSX, performance is lower.
If you select your games carefully and give the SLI combo a little more CPU power, then you will surely net a few extra frames. Here a couple of highlights: World in Conflict at 1920x1200 pixels with 4xAA on a single card yields 27.6 fps—with the GTX 260 in SLI it provides 43.3 fps (MSI’s overclock yields 44.5 fps). Mass Effect at 1920x1200 pixels and 8xAA with a single card delivers 49.3 fps, but the GTX 260 in SLI hits 72.8 fps (MSI’s overclock hits 77.8 fps).
When testing maximum power consumption, the fan of the GTX 260 reached its limit in SLI mode—the graphics processor throttles performance when temperatures exceed 105 degrees Celsius due to overheating. With a manually-configured 100 percent fan duty cycle and a noise level of 56 dB(A), the card reached its 105 degree ceiling without problems. The test system had a maximum power consumption of 610 watts, which then dropped to 490 to 505 watts as a result of thermal throttling.
With automatic fan control, a noise level of 55 dB(A) is reached and the computer can crash, but this does not always occur. As soon as the 105 degree limit is exceeded, the thermal GPU throttle starts up and a yellow warning LED starts to flash. Power consumption then fluctuates between 550 and 610 watts. Of course, in both of these situations, the system no longer runs at full 3D performance since the thermal throttle is only an unintended "energy saving" mode.
This overheating phenomenon also occurs with cards plugged in next to each other with no gap between them. For example, in a 3-way SLI setup employing a trio of Geforce 8800 Ultras, the gap between boards is too small and the graphics card fans are unable to draw in enough air. However, this is not just an Nvidia problem—the ATI X1950 XTX in CrossFire mode also cannot really survive without additional cooling. What does help is fresh air from the side provided by an 80 mm fan, which drops the GPU temperature of the GeForce GTX 260 SLI to 101 degrees.
The test for maximum power consumption is an extreme case that does not necessarily occur in real-world use. During normal game play, utilization fluctuates, only very rarely reaching the maximum value—as a result, the graphics chips have more time to cool down. If you wish to use the GTX cards for constant processing, you will soon feel the effects of the thermal limits and the restrictions of the cooling system.
The power consumption in 2D mode is 211 watts, while in 3D mode the top value with the entire system is 610 watts (power at the wall). If you wish to operate the GTX 260 OC in an SLI configuration, you will need a branded power supply with between 510 and 550 watts and 42 to 46 A on the 12 volt rail.