For basic overclocking, we wouldn't recommend messing around with voltages. Pump too much voltage into a GPU and you could damage it irreparably. Minor voltage bumps — say in the 1- to 2-millivolt range — are usually safe, but even then there are no guarantees.
Doing the deed
Before you start overclocking your graphics card, run some benchmarks to get a baseline for your unaltered system. We recommend Unigine's Heaven or Valley benchmarking tools. You can also run some in-game benchmarks if you'd like — all of the games tested in PCWorld's massive roundup of GeForce and Radeon GPUs include automated in-game benchmarks that make capturing repeatable data easy.
To use MSI Afterburner to overclock your graphics card, launch the utility and first crank up the power and temperature limits, though you may only be able to increase the power limit on a Radeon graphics card. A boost of 10% on the power target and a maximum temperature limit in the low- to mid-90's Celsius should work for most cards. If you're extremely risk-averse, you could leave both settings alone and continue with the process using the stock voltage and temperature settings, though that leaves potential performance on the table.
During the actual process of overclocking your graphics card, we recommend altering the GPU and memory clocks individually to isolate any possible instability.
Start slowly, increasing the core GPU clock frequency by 10MHz at a time. After you bump it up 10MHz, save the changes, then fire up the Heaven or Valley benchmark and look for system instability or graphical errors — odd color blobs, sparkling flashes of light, or other visual artifacts. If all looks good, bump the card up another 10MHz and repeat the process. Once you notice artifacts, dial it back a bit until they disappear. Jot down the final peak clock speed and reset it back to standard.
Now do the same for your graphics card's memory clock speed.
Once you know the peak frequency for both, set the GPU and memory to those speeds simultaneously and test for stability once again. If everything seems to be working well, go ahead and enjoy the fruits of your labor! If, however, your system has become unstable or you're seeing weird visual artifacts, back the frequencies down a few MHz for both, and test for stability or visual artifacts again.
If your system remains stable while overclocked, but performance actually decreases, reduce the GPU and memory frequencies until performance begins to scale properly. Overclocking a current-generation Nvidia GeForce GTX graphics card requires more tweaking and monitoring than previous products, for instance. that's mostly due to the automatic performance-tuning capabilities associated with Nvidia's GPU Boost, which dynamically increases the graphics card's clock speed until it hits a certain temperature.
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