Overclocking can get complicated, as you juggle all the variables. In addition to manipulating the power and GPU temperature targets, frequency offset values are used to further compound the clock speed increases that already come by way of GPU Boost. You'll occasionally find that increasing a certain clock frequency (or voltage) may seem to have worked properly, but performance actually decreases due to errors or throttling. You may also find that the actual GPU Boost clock may shoot above or below the designated offset value when the power and/or temperature targets are also increased. If you run into an issue overclocking an Nvidia GeForce card with GPU Boost, you'll just have to play with it until it's (safely) worked out.
The latest Radeon-based graphics cards give users the ability to alter power limits as well, but their clock frequency adjustments are more absolute. In other words, the GPU (or memory) will specifically target whatever clock speed you specify.
We saw measurable performance gains from both of the graphics cards we overclocked for this project.
The AMD Radeon R9 285 showed the biggest in-game performance increases, but the Nvidia GeForce GTX 960 saw the largest clock speed boost in sheer frequency gain. We tested the cards in an Intel Core i7-4960X powered system with 16GB of RAM, running Windows 8.1 Pro x64 and the latest drivers for each card. All tests were run at 1920x1200 resolution, with max image quality settings, and 4x anti-aliasing enabled.
To give you some concrete examples, Nvidia recommends a GPU boost clock of 1126MHz on the GeForce GTX 960. Factory overclocked cards usually boost into the 1300-1400MHz range. Simply by increasing the power and temperature targets in Afterburner, however, the card's GPU frequency regularly boosted into the 1450MHz range. Increasing the frequency offset and the GPU voltage resulted in an impressive 1538MHz peak GPU boost frequency. We also took the on-board memory up from 1752MHz to 1810MHz.
While overclocked, the performance of our GeForce GTX 960 increased measurably, though not majorly. The card's score in the Unigine Heaven benchmark, for example, increased from 916 (18 fps min., 36.2 fps average) to 946 (18.7 fps min., 37.1 fps average). Frame rates in BioShock Infinite and Sleeping Dogs jumped from 69.2 to 75.16, and 40.9 to 44.1 fps, respectively. With that increased performance also came higher power consumption, however. In its stock configuration, our test system pulled about 224 watts from the outlet under load, but that number went up to 246 watts after our tinkering.
The Radeon R9 285's performance increased more dramatically while overclocked. We took the card's GPU clock up from its stock frequency of 918MHz up to 1106MHz, and its memory from 1375MHz up to 1494MHz. In the Unigine Heaven benchmark, the Radeon's score jumped from 938 (17.2 fps min., 37.2 fps average) to 1029 (18.3 fps min., 40.9 average). BioShock's framerate increased from 72.51 to 79.34, and Sleeping Dog's framerate went from 42.8 to 47.6 — roughly a 10-percent increase in each game. Like the GeForce, power consumption went up quite a bit with the Radeon overclocked. Our test system pulled 354 watts from the wall with the Radeon R9 285 overclocked. At stock settings, it only pulled 304 watts.
Sign up for CIO Asia eNewsletters.