NVIDIA GTX 980 3-Way and 4-Way SLI Performance
Power Consumption, Sound and Closing Thoughts
Okay, we have looked at performance from a bunch of different angles, now let's compare power and sound levels of 4-Way SLI.
Our power testing was taken from Crysis 3; we obviously had to pick a game that had good scaling up through the 4-Way SLI results in order to make sure each GPU was being utilized as much as possible. First, the most interesting part of this for me is that even with a set of FOUR GeForce GTX 980 cards running simultaneously, this system only draw 689 watts at the wall! The idea that you could likely run a 4-Way GTX 980 system on an 850 watt power supply is mind blowing considering we needed 1200-1500 watt units for quad-GPU setups no that long ago. If you look back at my dual Radeon R9 295X2 Quad CrossFire story you'll see that system used 1261 watts at the wall - 83% more power than these four Maxwell GPUs at work.
Sound results are interesting as well, and could be confusing without some explanation. First, notice that the 2-Way SLI sound levels are only slightly louder than a single GPU, yet the 3-Way and 4-Way sound levels are MUCH higher. How can that be? Well, in our 2-Way configuration, the GTX 980 cards have a two-slot space of empty area between them, allowing both card to draw in cooler air much more easily. When you stack three or four cards right next to each other, the fans (on all but the bottom card) need to work a lot hard to bring in enough air to keep the GPUs at their expected temperatures. That means the fans much spin faster, generating more noise.
Remember that the GTX 980 reference cards had a partially removable back plate to make more room for air flow? As it turns out, the noise levels actually WENT UP in my testing when we took those off? I can't say for sure why but it appears that with those panels on, the air flow was "smoother" into the fan, generating less turbulence, and thus, noise.
Here is a comparison of fan speed and GPU temperature measured with both the back panel plate on (closed) and removed (open).
Fan speeds and temperatures were measured on the 2nd graphics card, sandwiched between the 1st and 3rd cards, the card that has the most issue remaining cool and calm under gaming pressure. You can see in the graph above that with the back plate open (removed) the fan is spinning around 400 RPM slower than with the back plate closed off.
In terms of real world temperature differences between an open and closed GTX 980 back plate, it is measurable. With the back plate on, even with the fan spinning 400 RPM faster (as seen in the graphic above) the GPU remains 3-4C hotter than with the back plate portion removed.
Looks like the designers were indeed onto something when they built in those removable back plates!
Multi-GPU gaming has always, and will likely always, present more problems to gamers than any single GPU solution will. With a single, fast GPU you will nearly always get 100% of your paid-for performance while going down the road of SLI or CrossFire always means there will be some sacrifice of individual GPU performance for the scalability you get. Our testing today with a set of four GeForce GTX 980 4GB reference cards proves that this is still indeed the case, despite claims from all parties involved that it would be better with this generation. Maybe it still can be, but drivers need to be optimized clearly.
Remember those graphs I showed you on the first page of this story? Now we have added to the "optimal" line the games we tested here today at the 4K resolution. The closer each line is to the blue line, the better the scaling of SLI in that particular title. For example, both Sniper Elite 3 and Crysis 3 do very well at 2-Way, 3-Way and 4-Way SLI. However, a game like Metro: Last Light or even Bioshock Infinite shows very little scaling beyond 2-card configurations.
Nearly all of the games we tested were able to show relevant and useful scaling with two GPUs and do so without a major increase in frame time variance that would lead to a stuttery, messy gaming experience. Nothing's perfect, and games like Bioshock Infinite and Skyrim don't give you the extra performance that you might expect out of the box. But more demanding games like Crysis 3, Metro: Last Light and even Battlefield 4 proved that dual GTX 980s can work very well and provided added performance for high resolution displays or gamers that want to hit peak frame rates.
NVIDIA's fancy SLI bridges only support 3-Way SLI
But when we stretched to 3-Way and 4-Way SLI, only Crysis 3 and Sniper Elite 3 really provided any indication that using more than the two graphics cards was a worthwhile venture. Those two games showed expected scaling rates of 90%, 39% and 29% as you go up the multi-GPU ladder. That means for a second investment of $550 (the cost of another GTX 980) you will get 90% added performance. Another $550 investment nets you another 39%, while a fourth payment of $550 only gets you 29% more. Even when 4-Way SLI works well, the value proposition is tough to argue for.
But I guess that was never the intent. 4-Way SLI users are a rare group and I would argue that they pile on the GPUs more for show and the occasional kick ass gaming performance rather than for constant, improved gameplay. At least I hope that's why they do it, because otherwise they are kidding themselves.
I can't deny that seeing a stack of four GTX 980 cards in a system makes me anything but nervously excited, I just don't think I would recommend actually shell out the money for a configuration of their own.