Overclocking, Temperature, Noise & Power Use
Let's get one major truth out of the way right from the start: the success or failure of overclocking video cards has a whole lot more to do with luck of the draw, also known as the "silicon lottery", then it does the design of a card's circuit board and cooler. Yes, you can read all about the huge number of power phases and massive thermal capacity of coolers, but with its current GPUs, Nvidia has pushed the art of fine-tuning to the limit, such that there's just not a lot of overclocking headroom left on the table. That's great for gamers, but maybe a bit of a letdown for overclocking enthusiasts. The reality is that most Pascal-based GPUs will achieve an overclock of 10-13%, depending on the quality of the GPU, not the quality of the cooler or circuit board.
So, with that said, let's get to the numbers. We had two reference-based GTX 1080 Ti Founders Edition cards, and both maxed out around +160MHz on the core and +800MHz on the memory. What this translates to in games is 2000MHz on the core and 11,800MHz on the memory, at least nominally. In reality, the core clock is heavily impacted by temperatures and power limits, so when people brag about the overclock they can hit, they're talking about something they'll never see in a game for more than a few seconds. Our reference cards clocked at "2000MHz" actually averaged about 1924MHz in games, because they hit the thermal throttle point almost immediately.
The good news is that our Hybrid cooler was able to unleash a whole lot more headroom in our overclocks. While adding additional voltage did not provide any additional headroom, we were able to get all the way up to +175MHz on the core, just due to the lower leakage offered by lower temperatures. And much more importantly, with the Hybrid cooler attached, our GPU simply stopped thermal throttling. In games, our 2012MHz overclock actually ran at 2000-2012MHz, limited only by power. Even maxed out at the 120% power limit allowed by Nvidia, this overclock did indeed hit a throttling point, and it had nothing at all to do with temperatures. Let's look at some of the data we collected to get to provide a bit more perspective on overclocking.
For many GPU enthusiasts, the graph above may be all that needs to be said on the subject of GPU cooling. Our load test used The Witcher 3, and even with a big overclock, our GTX 1080 Ti with a Hybrid cooler attached hit just 56 °C, compared to the 87 °C the reference card hit. Note that this is with the thermal and power limits lifted as high as they would go using the MSI Afterburner utility (90 °C and 120%, respectively). Our non-OC numbers were gathered using zero tweaking, which means both power and temperature limits were in full effect. That's why the reference GTX 1080 Ti only hits 84 °C, the limit imposed by Nvidia.
There's just one fly in the ointment, and that's noise. The EVGA Hybrid cooler is incredibly loud, easily drowning out the noise generated by our dual-120mm Corsair Hydro CPU Cooler. While pump noise is usually the main problem when it comes to liquid cooling, in this case it's the 120mm fan supplied by EVGA. It starts at a buzzy 1,100RPM and just goes up from there. It's shockingly-loud, really. We actually performed some testing using a high-end Scythe cooler locked at 1,200RPM, and we found that idle noise dropped to just over 40dB, which is a whole lot more acceptable. Yes, load temperatures went up a bit, but in our opinion, that's a fine tradeoff. Any enthusiasts looking to GPU liquid cooling to tame the noise from their systems will absolutely need to switch out the fan supplied by EVGA. Note that it has an ultra-short custom power lead, so it can't even be hooked up to a motherboard for more fine-grained user control.
In contrast to our temperature and noise numbers, there's relatively little to say about power. We were actually very impressed that the Hybrid cooler didn't negatively affect idle power use, and in fact seemed to have an overall positive effect on load power use, coming in just slightly below the Founders Edition in nearly all our gaming runs. This is particularly impressive in the context of our OC numbers, as the GTX 1080 Ti with the Hybrid cooler not only hit a slightly higher nominal overclock, it also ran about 75MHz due to the total absence of thermal throttling. In other words, you're getting a faster result despite the same or lower power use. Very cool!