Overclocking, Temperature, Noise And Power
Before adjusting any settings, we ran 3DMark at the Hydro GFX's stock clock rates to get a baseline score. Right off the bat, Corsair's card scored 16,638 on 3DMark with a graphics score of 19,791. Those numbers seemed high, so we re-ran the test with GPU-Z logging the board's vital signs. Upon reviewing the log, we found that the Hydro GFX was hitting GPU Boost clocks as high as 1429.4MHz out of the box.
Next, we turned the temperature and power limits to their maximum allowed levels. The 91 °C thermal ceiling never came into play; Corsair's H55 cooler kept the GM200 under 60 °C. The more forgiving power limit is what we were really after. Our 3DMark numbers rose again, demonstrating no ill effects from our changes.
We started by tweaking the GPU clock rate. Given the high GPU Boost frequency previously observed, we jumped in 25MHz increments. Once we hit a base clock rate of 1265MHz, our increases shrank to 5MHz. After dialing in each new setting, we ran 3DMark Fire Strike to test stability.
Over time, we determined that a 1370MHz base (80MHz higher than stock) was as far as we could go without a voltage increase. Beyond that, 3DMark would crash mid-run.
With ample thermal headroom, we started to increase the voltage using MSI Afterburner, hoping to stabilize an even more aggressive overclock. As a test, we dropped the frequencies back to their stock levels and starting increasing voltage in 10mV steps, again running 3DMark after making each change. Higher than 70mV, performance started to drop, so we used that as our voltage offset and went back to work on the GPU clock rate. Ultimately, we managed to get a stable (or so we thought) 1278MHz base frequency with GPU Boost rated at 1379MHz. What we actually observed during our test run was a significantly higher 1518MHz, though.
With the GPU dialed in, we moved on to memory. Corsair stressed that the GDDR5 it uses should overclock to 8 GT/s without trouble, so we took the company up on the challenge. Starting with the GPU at its stock frequency, we gradually cranked the memory up to 8080 MT/s. That was a stable setting on its own. But with the GPU overclocked as well, Corsair's card wasn't stable (it locked up in our Battlefield 4 temperature test).
Ultimately, we found a compromise with the GPU set to 1260MHz, GPU Boost at 1361MHz and the memory at 7896 MT/s. The GPU Boost frequency we observed in practice was closer to 1500MHz, though.
Unsurprisingly, Corsair's Hydro GFX runs much cooler than its competition. We've seen liquid cooling used quite effectively several times before in the graphics world, and Corsair's H55 appears to be a good match for Nvidia's GM200 GPU.
The idle temperature we measured is slightly lower than Gigabyte's GeForce GTX 980 Ti Xtreme Gaming with its always-on fan profile. Further, Corsair's Hydro GFX is nearly 10 °C cooler than PowerColor's water-cooled Devil R9 390X.
Even after 10 minutes under load, the Hydro GFX remains several degrees cooler than PowerColor's card. In fact, at no time does the GPU reach the 60-degree threshold that triggers the fans on most air-cooled cards.
Because the Hydro GFX employs a hybrid cooler, there are several components that can generate noise: the axial fan on the radiator, the pump and the card's centrifugal fan. We measured acoustic output next to the radiator and from behind the graphics card, but our instrument didn't pick up a reading from the radiator so we didn't add that to the chart.
From behind the card, even at idle, the decibel meter registered 36 dB(A). We attribute this to the always-on blower-style fan. But after 10 minutes of gaming, the board remained relatively quiet. Gigabyte's GeForce GTX 980 Ti Xtreme Gaming is slightly less noisy, but Corsair's temperature advantage justifies its slight deficit in our acoustic measurements. And at least the Hydro GFX is a lot quieter than PowerColor's liquid-cooled R9 390X Devil.
In a recent GTX 980 Ti review, we were surprised by higher-than-expected power consumption. Not long after, our colleague from Germany, Igor Wallossek discovered that Nvidia drivers released after version 355.65 have a bug with X99 systems that cause higher power consumption. With an older driver package installed, the Hydro GFX lands right around 18.1 watts.
Corsair's card may behave itself at idle, but it gets power-hungry in 3D workloads. Our measurements suggest that, in stock form, the card draws 267W in Battlefield 4. Overclocked, that number jumps to 276W. Sapphire's R9 Fury Tri-X OC ducks in at 258W in the same metric.
Curiously, the Hydro GFX uses less power than Gigabyte's GeForce GTX 980 Ti Xtreme Gaming in FurMark. In stock form, Gigabyte's card draws 19W more than Corsair's board after it was overclocked.