Radeon HD 5770, Radeon HD 4890, And GeForce GTX 275 Overclocked

MSI N275GTX Lightning: Fully Overclocked

Now it’s time for our own little warning: overclocking can damage your hardware and void your warranty. However, there are some good rules of thumb to help you prevent frying your graphics board. Usually, you can increase a card’s default clock speed by another five to ten percent. Don’t jump to the highest setting immediately. Instead, increase the frequency in increments of 5 or 10 MHz and test stability. Also, don’t try to change all settings at once. Find the highest stable frequency for the GPU, then move on to the shader, followed by the memory.

We recommend using a graphically-demanding game that puts a lot of strain on the GPU to test your settings. Anything with the Unreal 3 engine should work well (Ed.: here at the Tom's Hardware US office, we like to use FurMark for stress testing). Select a high resolution (ideally 1920x1200), turn off anti-aliasing and enable anisotropic filtering. If the game freezes, that usually means the GPU frequency is too high, while visual artifacts and rendering errors tend to mean the memory can’t cope with the selected clock speed. Lower the speeds immediately in either case. Finally, if you get a DirectX error, chances are your shader clock was set too optimistically.

MSI’s factory overclocked settings work flawlessly. However, we encountered several problems when we attempted to overclock the card. Since MSI’s own OC tool wouldn’t let us adjust the shader clock, we used eVGA’s Precision tool instead, with a goal to achieve the highest clock speed possible that didn’t require a voltage tweak. That turned out to be more difficult than it sounds, since our combination of Windows Vista, Forceware 191.07, and MSI’s Lightning Afterburner software turned out to be a little, let’s say, touchy. If the overclocked settings don’t work, Windows Vista kills and restarts the graphics driver, after which the card only runs at half speed. The only way to get out of this 400 MHz mode is to reboot the system.

After half a day of experimenting with various clock speed combinations, we found 720/1,600/1,200 MHz (GPU/shader/memory) to be the safest, most stable settings. Interestingly, the 1,200 MHz memory speed corresponds to the highest setting in MSI’s Lightning tool.

In order to increase the GPU speed further, we had to perform a little ritual in a specific order. Start MSI’s OC tool, raise the voltage, then launch Precision to overwrite MSI’s clock speeds. This took several more hours, partly because MSI’s utility proved to be very dominant. Switching to another performance preset or using one of the Lightning utility’s frequency sliders immediately overwrites any settings selected through Precision. Then, if you choose a clock speed that is too high, the system will freeze or the graphics driver will reset itself, restarting in 400 MHz mode. Either way, you’re forced to reboot the system.

Raising the voltage a little from 1.0665 to 1.0790 V allowed us to push the GPU as far as 770 MHz. Remember, Nvidia’s reference speed is 633 MHz, while the GTX 275 Lightning has a stock clock of 700 MHz. This setting wasn’t without its problems, though, as the system would become unstable under load. Additionally, 1,600 MHz was no longer a viable option for the shader, and we had to reduce the memory frequency to 1,170 MHz as well. After lots of trial and error, we ended up at 770/1,550/1,170 (GPU/shader/memory). Since the lower shader and memory speeds negate any improvement achieved through a faster GPU clock, we decided to take a step back and stick with the settings achieved without a voltage tweak (720/1,600/1,200 MHz).

At MSI’s factory overclocked settings, the GPU runs 10.6 percent faster than a reference card. The 1.4 percent increase in memory speed is negligible, though, and the shader frequency isn’t changed at all. Overall, that gives our card a performance boost of 5.5 percent. According to the retail box, MSI’s overclocked NGTX275 Lightning is supposed to perform on par with a GeForce GTX 285. We can’t really refute that claim, since it all depends on the benchmarks, CPU, and graphics driver version MSI used. Based on our own hardware, we still saw a performance gap of one to two percent.

Our maximum overclock made the situation much clearer, with the GeForce GTX 275 effortlessly reaching performance levels similar to those of a reference GeForce GTX 285. If MSI had also pre-overclocked the shader, this would be a really great card. As it is, the NGTX275 Lightning is a card with a very quiet dual-fan cooler, a very potent graphics chip, and a dubious overclocking tool that doesn’t harness the full power of the hardware. If you buy the GTX 275 Lightning, we would actually recommend not installing the Lightning Afterburner tool at all and using the stock (overclocked) settings instead. If you still feel the need to tweak the memory and shader speeds, use eVGA’s Precision utility instead. But beware that you do so at your own risk.

To end on a positive note, we did like that overclocking did not affect the card’s 2D mode, letting the board idle at 300/600/100 MHz.

Since MSI equips the GTX 275 Lightning with twice as much memory as a reference card, we also tested the card at Nvidia’s reference speeds (labeled No OC) to see whether there was a performance difference compared to cards with only 896MB of memory. As you can see in our table, the larger memory size offers no benefit over the standard configuration in overall performance. On the other hand, certain games (like Grand Theft Auto IV) can be run at higher detail settings with the larger frame buffer.

With the current generation of drivers, we also encountered some stuttering in Fallout 3, with the scene freezing for a short moment when you turn. Interestingly, this was not a problem with the older GeForce 186 generation, and only seems to plague the combined releases for Windows 7 and Vista.