In terms of performance, we had a rough idea of what to expect based on the specifications AMD had sent to us with weeks of anticipation. What we have here is a pair of slightly diluted Radeon HD 6970 GPUs squeezed onto a single PCB. With core clock speeds reduced by 6% and the memory frequency lowered by 9%, on average the Radeon HD 6990 was 6% slower than two Radeon HD 6970 Crossfire graphics cards.
Power consumption figures did surprise us, having the Radeon HD 6990 suck down 15% less power under load when compared to the Radeon HD 6970 Crossfire graphics cards. Despite being the most power hungry single graphics card on the planet, the Radeon HD 6990 is actually very efficient, more so than the Nvidia GeForce GTX 580, for example.
Out of the 14 games that we tested with, the Radeon HD 6990 was on average 48% faster than the GeForce GTX 580 and 46% faster than the Radeon HD 5970. It was also 66% faster than a single Radeon HD 6970, with Crossfire scaling well on most scenarios.
While this all sounds very positive, we consider the steep $700 price tag to be a showstopper. Although having a single graphics card can be convenient, its hard to justify a price premium for the luxury when two separate cards are not only cheaper but also a bit faster. About the same level of performance can be achieved with a pair of Radeon HD 6950 graphics cards for $100 less. Meanwhile, most of these cards can be unlocked to HD 6970 specifications making them a seriously good value.
Moreover, like all multi-GPU graphics cards, the Radeon HD 6990 relies heavily on driver support to perform as intended. Every time a new game is released it's likely that the Radeon HD 6990 will not fully support it (taking advantage of the two GPUs) until AMD updates the Catalyst driver. Without full Crossfire support, the Radeon HD 6990 will perform somewhere in between a single Radeon HD 6970 and 6950 graphics card, which is pretty decent but not worthy of $700.
Make it official, the Radeon HD 6990 is hands down the fastest graphics card on the market, outperforming previous generation dual-GPU products by a long shot.
Now, we can't decide for you whether it makes sense to spend $700 on this graphics card or not. Its certainly nice having the option. But as far as we are concerned even a $600 price point would have made us think twice about the different alternatives unless say, you are building a monster rig worthy of quad GPUs.
Never mind what we believe, already there are a few cards floating around in retail, though it seems finding a Radeon HD 6990 for $700 won't be easy with most up around $740.
Update - Dual-BIOS support: Some of you noticed we didn't mention one of the Radeon HD 6990's unique features. Dual-BIOS support can be toggled from a physical unlocking switch on the card, which switches between the factory-supported BIOS of 375W (tested throughout this review) and an "Extreme Performance BIOS" that boosts core clock speed from 830MHz to 880MHz and in the process throttles power consumption to a staggering 450W. What you should know: performance difference was negligible when overclocking the card.