NVIDIA GeForce GTX 980 SLI Overclocked GPU Review

We take 2-Way GeForce GTX 980 SLI and overclock both video cards. While we are at it, let's also overclock Radeon R9 290X CrossFire and GeForce GTX 780 Ti SLI. Once we get these clocked to the highest rates we could reach, let's see how these all compare at 4K resolution, NV Surround, and AMD Eyefinity.


Overclocking GTX 980 SLI

We utilized the latest version of MSI Afterburner as our choice for overclocking software with the two reference GeForce GTX 980 video cards. We made sure the option was selected to synchronize settings between similar GPUs so that manipulating the sliders would affect both GPUs. We also turned on the on screen display in games and watched for consistent clock frequency, voltage, and temperatures.

Before we can look at what we found as the highest overclock we first needed to find out where we were starting from with GTX 980 SLI. We found that GTX 980 SLI behaves differently than one single GeForce GTX 980 GPU in terms of in-game real-time clock speed and voltages as you might expect.

We found that the voltage seemed to always differ between GPU1 and GPU2 while in SLI. At all times GPU2 was operating at a lesser voltage, and lesser GPU temperature compared to GPU1 while in SLI. An example of the voltage difference is: GPU1 - 1.168v, GPU2 - 1.112v. The voltage was also very dynamic, meaning it changed almost every second as we moved through the games. It was impossible to find the "average" voltage, because the voltage varied greatly. Note, the other video card comparisons also had differing voltages.

We found that with the default settings on GeForce GTX 980 SLI the lowest clock rate it hit while in-game was 1126MHz. That clock speed is actually below the boost clock of 1216MHz for GTX 980. This is the first time we've seen the real-time in-game clock speed clock throttle below the boost clock in SLI in games. It seems GTX 980 SLI is clock throttling in SLI on reference video cards. This is something we did NOT expect, but it is happening with reference cards. This begs the question which we will have to answer another day, "Will this happen with custom cooled video cards?"

We noticed that when the GPUs would hit 80c the thermal throttling in SLI would occur and drop the clock speed from the boost clock. We know that it is strictly temperature that is causing this clock throttling in SLI because we also tried a test by just raising the fans to 100% fan speed. When we did this the in-game clock frequency jumped to 1266MHz consistently without dropping.

So this goes to prove, the reference cooler on the reference GTX 980 cards is causing thermal throttling. Raising the fan speed manually does fix the issue and provides a clock speed above the boost clock in games. So if you want a fast and easy overclock, just raise the fan speeds.

Our starting point with the cards at default settings is 1126MHz (Auto Fan Speed) and we note thermal throttling at 80c. Turning the fans to 100% takes the clock speed up to a consistent 1266MHz on both GPUs while gaming. So since we are going to overclock with a 100% fan speed for these reference cards, we will use 1266MHz as our starting clock.

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Our final overclock was to push the core clock to +200 on both GPUs and the memory to +400 with the maximum power limit of 125. Raising the voltage only pushed the GPUs past the TDP and caused clock throttling. This is with a 100% fan on both cards, which is very loud. If you are curious what the ASIC Quality is, GPUz reports: 71.3% and 81.8%.

What does that actually result to in games? It comes out to be 1466MHz and 7.8GHz memory. In actuality however, the clock speed did fluctuate between 1452MHz to 1466MHz in some games. In some games it was a steady 1466MHz, in some games it was 1460MHz, in one it went down to 1452MHz.

We noted that the maximum GPU1 voltage was 1.218v and GPU2 was 1.150v. We saw this voltage and clock speed remain consistent, which seems a bit odd, but it was stable. GPU1 would run at 1.218v and 1466MHz and GPU2 would be at 1.150v and 1466MHz consistently. We watched very intently to see if GPU2's clock speed would fluctuate operating at a lower voltage, but it did not. These were very stable settings.

Our final stable overclock is 1466MHz / 7.8GHz on both GPUs.