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Conclusions
AMD has built a mighty fine piece of hardware in the Radeon HD 7990. Consistently high FPS averages attest to its potential as the single most powerful graphics card in the world. At the same time, the 7990 is exceptionally quiet under load. Throw in the fact that it ships with a ridiculous bundle packed with some of the most notable games of the past year, and it's easy to see how the 7990 could grab the crown in the $1K graphics card market.

However, we've deployed some advanced tools and metrics to answer some very practical questions about the benefits of the 7990's second GPU, and the answers haven't turned out like one would hope. The card just doesn't hold up well under the weight of really tough scenarios where smooth gameplay is threatened. The 7990 does perform a little bit better than its single-GPU counterpart, the Radeon HD 7970, in our Crysis 3 test, but not by a broad margin. The 7990 doesn't offer an appreciable benefit over the 7970 in our Tomb Raider and Sleeping Dogs test scenarios. In each of these cases, the 7990's FPS averages scale to nearly twice the 7970's, but the uneven frame delivery caused by multi-GPU microstuttering blunts the impact of those additional frames. Worse still, the 7990 runs into some apparent CrossFire compatibility snafus in Far Cry 3 and BioShock Infinite, both AAA titles that AMD has co-marketed and bundled with the card itself. Yikes. In those two games, you're literally better off playing with a Radeon HD 7970.

Sure, we're only talking about five games, tested under specific conditions. But we created these conditions in order to answer a pressing question about the impact of multi-GPU microstuttering. We've had the tools to detect its presence for a little while, but does microstuttering really have a negative impact on gameplay? The answer appears to be yes. Also, microstuttering tends to grow worse as frame rates drop, calling into question the true value of multi-GPU schemes like CrossFire and SLI.

Nvidia has mitigated the effects of multi-GPU jitter via its frame metering capability, and that feature appears to work reasonably well most of the time. The GeForce GTX 690 is tangibly superior to the single-GPU GeForce GTX 680 in each of our test scenes, although the difference is pretty minor in Crysis 3. That case is a reminder that frame metering and pacing schemes aren't perfect. The 690 has near-pristine frame delivery in Crysis 3, but the smoothness of the animation is compromised by a see-saw pattern of frame dispatch, as we measured with Fraps. Fortunately, such early-in-the-pipeline jitter is usually confined to small spans of time—just a handful of milliseconds—on the GTX 690 and similar frame-metered SLI solutions.

AMD is now following suit with the development of a frame-pacing feature in its drivers, and the early returns look promising. If the firm can follow through and deliver a production driver that includes this capability, the 7990 has the potential to become a more appealing product. The thing is, that driver isn't here yet, and we don't know when it's coming. Radeon HD 7990 cards are due to hit store shelves a little more than a week from now. My advice to would-be buyers is to hold out until a final driver with frame pacing has been released, tested thoroughly, and found to be effective. In its current form, there's no way the 7990 is deserving of its $1K price tag.

Maybe I'll post this whole review on Twitter, bit by bit.TR
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