Overclocking and Cooling Performance
For our overclocking test, we enabled the hidden overclocking features built into the NVIDIA control panel by using Coolbits. When using NVIDIA's built in clock speed detector, the ASUS Extreme GeForce N6600GT Silencer was overclocked to 525MHz on the core, and 1.07GHz on the memory. This maximum clock speed detector is usually a bit conservative with it's overclock though, so we decided to see how far this card could actually go. We used ATI Tool's artifact detector for our test. While it's mainly for ATI cards, the artifact detector can be used with either ATI or NVIDIA cards as well, and will usually detect artifacts with it's testing, even before you'd notice them while gaming.
With the core set to 525MHz, and the memory set at it's default 1GHz, we ran ATI Tool for 15 minutes at stock settings to let the card heat up. Once the 15 minute mark was reached, we started raising the core by 5MHz about every 2 minutes until artifacts started to appear. At 540MHz, we had reached our limit. We would have liked to go higher, but the card wouldn't have any of that. We used a similar procedure when overclocking the memory. After letting the card heat up at 1.07GHz, we raised the memory by 10MHz every 2 minutes, until the test started displaying errors at 1.11GHz. This is much more impressive than our core overclock. We then set the card's core to 540MHz and the memory to 1.11GHz simultaneously and benchmarked for 25 minutes without an error. To give you an idea of the performance improvement that our overclock has brought, we decided to benchmark Quake 4 again at 1280x1024 with no Anti Aliasing, and 4x Anisotropic Filtering.
With an increase of 6.4FPS, Quake 4 becomes a little more playable at 1280x1024 with no AA and 4x AF applied. No matter how cool the core was, we couldn't get it to go past 540MHz without artifacts in ATI Tool. While NVIDIA's driver level artifact tester didn't report any problems until around 555MHz on the core, we opted to keep it at 540MHz for the sake of the card's longevity. ASUS does not provide any kind of overclocking with its warranty, so it's up to you to decide if the extra FPS is worth the punishment to your card. Those of you with minimal airflow in your case probably shouldn't overclock this card at all. That is only our recommendation, however, and each personal case will be different. It's really up to each individual consumer to weigh the risks against the benefits of overclocking with a passive heat sink. If you have any questions about overclocking, make sure to visit our PCHardware Forum for discussion on the subject.
Well, we have some interesting results here. The large heat sink that ASUS has used is able to disperse a great amount of heat. When having a small table fan near the card, blowing directly on the copper fins, the core only manages to reach a temperature of 62'C at full load. When moving the card into our Gigabyte 3D Aurora case, the load temps jump to around 78'C at full load. This is hot, but not nearly as hot as the results from our open air test. With our motherboard laying on our test bed, with no active airflow, the ASUS Extreme N6600GT Silencer jumps to 85'C. Now, you must remember that this is with the motherboard and video card out in the open. If you were to install this card inside a case with other components such as a motherboard, hard drive, and CPU installed, we could see the card reaching close to 90'C, possibly more.
We really can't stress enough how important airflow is in a computer case. The quest for a silent system will always stop short of complete silence. We have to recommend that at least one additional fan be installed in your case should you plan to use this card. Simply having hot air removed by the fan inside your power supply probably won't be enough to keep this card reasonably cool.