SLI vs CrossFire: Which Dual-Card Setup is the Best?
We look at dual card graphics and PC gaming. When you add a second card, which cards are faster? Which scale better? And which can you actually stand to have in your system?
Graphics cards have gotten faster and added more features. So we have to ask the question: is it really worth adding a second GPU to your system? Will you get enough of a performance boost to justify the extra power draw and added cost? The answer is more complex than a simple yes or no. It all depends on what games you’re running, how much you dial up features like anti-aliasing, whether you’ve dived into the world of stereoscopic 3D and what monitor you’re running.
Perhaps the most important factor in the decision is display resolution. If you’re running a 1680x1050, 22-inch display, a single midrange or high end card will get the job done. Adding a second GPU is overkill. If you’ve got a 30-inch, 2560x1600 display and want to crank up the AA and postprocessing features, then that second GPU can be a big help.

Stereoscopic 3D, like Nvidia’s 3D Vision, demands more performance as well, since you’re effectively doubling the frame rate requirements of a game. Most 3D displays currently available max out at 1920x1080, however, so the performance demands aren’t overly onerous.
Games themselves are evolving and adding more features. You can see that in a title like Just Cause 2. Still a DirectX 10 title (and it requires DX10 or higher), Just Cause 2 adds a host of postprocessing effects that can demand much from your graphics card. Toss in DX11 titles, like Aliens versus Predator or STALKER: Call of Pripyat, and frame rates can plummet as you add features. So that second GPU can indeed contribute to the overall experience.
With these thoughts in mind, let’s take a look at our SLI and CrossFire X candidates.
The Cards
We looked at seven different DirectX 11 capable cards, including four based on Nvidia GPUs and three using AMD graphics chips. We also tossed in the fastest single GPU card from the previous generation, Nvidia’s 285 GTX, in the form of a pair of eVGA GeForce 285 GTX SSC cards. Note that not all cards were identical. With the exception of the GTX 460 768MB, Radeon HD 5870 and GeForce GTX 480, all were run at reference speeds. The GTX 460s, HD 5870s and GTX 480s were factory overclocked by a few percentage points, as were the previous generation 285 GTX cards.
Here’s the lineup; note there were two of each, and we call out the models where appropriate.
- A pair of Asus 768MB GTX 460
- One Gigabyte GTX 460 1GB card and one reference GTX 460 1GB
- One eVGA 470 GTX card, one Galaxy GTX 470
- A pair of eVGA 480 GTX SC cards
- One Radeon HD 5830 reference card, one XFX Radeon HD 5830
- One Asus Radeon HD 5850 and one XFX Radeon HD 5850
- One HIS Radeon HD 5870 Modern Warfare 2 Edition and one XFX Radeon HD 5870 XXX Edition. These are both 1GB, factory overclocked cards.
While the core and memory speeds of some of these cards may be higher than stock reference cards, it’s been our experience that actual game performance increases only slightly. So we can still make judgment calls on performance, even though all of these aren’t stock cards.
Our test bed is a 3.33GHz Core i7-975 Extreme Edition in an Asus P6X58D Premium motherboard with 6GB of DDR3/1333 and a Corsair TX850W PSU. The OS is 64-bit Windows Ultimate. All games were run at 1920x1200 with 4x AA. In point of fact, we ran at 2560x1600 with and without AA. But our tests were still pretty demanding at 1920x1200, with 4x AA and all eye candy cranked up. So those are the results we’re reporting here.
We installed the latest release drivers -- 258.96 WHQL for Nvidia and Catalyst 10.7 for AMD. We also made sure each card’s dual GPU feature was enabled. AMD will enable CrossFire X by default if it detects two cards, while you’ll have to manually turn on SLI with Nvidia cards.

Make sure you manually enable SLI in the Nvidia control panel
Let's dive right in.
DirectX 10 Gaming
First, let’s take a look at games and benchmarks that run on DirectX 10. This allows us to see how much we’ve gained since last generation. We’re using the fastest single GPU card from last generation, a (once) speedy eVGA GeForce 285 GTX SSC, factory overclocked to 702MHz (versus the stock 648MHz) core and 2646MHz memory (the stock memory clocks are 2484MHz.) Let’s see how the new kids on the block handle the now geriatric 285 GTX:

First up is the hoary old 3DMark Vantage, running the “extreme” test. The older 285 GTX just wins out over the newer Radeon HD 5830, but falls short of everything else. Note how even two GTX 460 768MB cards, with their relatively low memory bandwidth, still spanks the older card.

Crysis is still a demanding test, even after three years. Just when you begin to believe it’s CPU bound, tossing in a second, new generation card pumps up the frame rate. A pair of GTX 480s are the overall winner, just falling short of the magical 60fps. It’s impressive how the $230 cards – GTX 460s and Radeon HD 5830s – generally keep up with the once mighty 285 GTX.
Next up is a pair of Far Cry 2 benchmarks.


The longer Ranch benchmark was once a demanding GPU test, but it’s become pretty easy by today’s standards. Once again, AMD’s Radeon HD 5830 is the odd duck, but note how even the low cost 460 GTXs are essentially at performance parity with the pricier Radeons in this graphics intensive test.
Far Cry 2’s action benchmark is more indicative of actual gameplay, so the test is CPU limited on higher end cards – in this case, anything that’s not an older card (285 GTX) or memory limited (GTX 460 768MB). Note how tight the grouping is here – that’s because the benchmark throws of ton of physics around, plus numerous AI characters running around trying to kill you. We wouldn’t make any graphics card decisions based on this benchmark, but it’s worth noting that GPUs aren’t the entire ball of was in PC gaming.

Tom Clancy’s HAWX is an action flight sim; we used the DirectX 10 version in our testing. Once again, AMD’s Radeon HD 5830 is the weak sauce, illustrating what an odd duck AMD’s lower end midrange card really is. While the HD 5870 wins out over the two GTX 460 cards, it’s no match for the paired GTX 470s or 480s.

Just Cause 2 is one of the few titles that requires DirectX 10 as a minimum, as well as running only on Windows Vista or Windows 7. The Concrete Jungle test throws a lot of postprocessing effects at the card, and can hammer frame rate – and it’s not particularly CPU bound. Note that we disabled the Nvidia-specific Bokeh and water effects to keep the playing field even.
AMD stays in the game with Just Cause 2, at least with paired Radeon HD 5870s. The Radeon HD 5830 and 5850s don’t fare quite as well. Once again, the 5830 is the weak sister of the bunch.
Next Page: DirectX 11 Benchmarks...