Performance: Quad-SLI Versus Quad-CrossFire
Just prior to the launch, Maingear sent over its gorgeous Shift, all decked out with an overclocked Core i7-2600K running at 4.5 GHz. It included two GeForce GTX 590s and one Radeon HD 6990 (we already had one here in the lab to add to the system), allowing us to run benchmarks in an actual case and compare quad-GPU configurations from both AMD and Nvidia.
Maingear helped assuage one of my biggest concerns with its machine: mainly, the need for ventilation would force enthusiasts to adopt ugly, airy enclosures just to let the cards inside breathe. The Shift demonstrates that it's still possible to get a classy, monolithic PC (vertically-oriented, even) and still support GeForce GTX 590s and Radeon HD 6990 cards in quad-GPU configurations. The system does radiate a lot of heat under load, particularly toward the bottom, where these cards push a lot of air, but it handles the challenging thermals without a hiccup.
Most impressive is the fact that both configurations work without generating a ton of noise. Do not compare the following numbers to the results on page 17. Instead of measuring from 28" behind each card's exhaust port, we buttoned up the Maingear machine, stuck it under a desk three feet away, and noted the acoustic levels two feet off of the ground.
|Noise At Idle And Load (Extech 407768)|
|GeForce GTX 590 3 GB (Quad-SLI)||Radeon HD 6990 4 GB (Quad-CrossFire)|
|Idle||43.9 dB(A)||43.5 dB(A)|
|Load||48.2 dB(A)||53.2 dB(A)|
The AMD cards are still louder than Nvidia's in a closed system versus an open test bench. However, we're pleased to see Maingear's beefed-up cooling subsystem keeping air moving briskly enough to avoid the 3600 RPM fan setting.
Now we can start comparing the performance of two Radeon HD 6990s to a pair of GeForce GTX 590s. Just as we saw in the single-card results, Nvidia's flagship part dominates, so long as you don't exceed the capabilities of its onboard memory. With 4x MSAA applied, AMD's Radeon HD 6990 in one- and two-card configurations is the faster solution. And you really need two of those cards (four Cayman GPUs total) to make Metro 2033 playable at 2560x1600 using our demanding settings.
Although AMD gets the upper-hand in the most taxing environments, we get the sense that its drivers aren't yet as ready for quad-GPU operation, despite the almost three-week head start its team has on Nvidia's launch. Two 6990s in CrossFire aren't even able to start the Lost Planet 2 benchmark before crashing to the Windows desktop.
AMD's problems continue in Aliens vs. Predator, where even its newest Catalyst 11.4 preview driver doesn't seem to serve up scaling between two cards. As a result, where we see one Radeon HD 6990 outperform the GeForce GTX 590, two 590s take a commanding lead.
In single-card mode, AMD's Radeon HD 6990 is only slightly faster than the GeForce GTX 590. But adding a second card shows that four Cayman GPUs scale better than a quartet of GF110s in Battlefield: Bad Company 2.
One Radeon HD 6990 is faster than one GeForce GTX 590 in Just Cause 2. Adding a second card allows AMD to maintain that lead without AA/AF. However, the GeForce GTX 590s in SLI manage to pass AMD's solution once anti-aliasing is applied. The performance is close, just as we'd expect given identical price tags.