The only caveat we'll add to the performance discussion is that because this is a dual-chip card, it relies on the scalability of 3D games to put both chips to good use. If a game or the card's driver software falters, you may see limited performance. Two recent cases in point: Far Cry 2 had an issue with cards using ATI's CrossFire multichip technology (since resolved), and as of this writing, the PC version of Grand Theft Auto IV won't recognize Nvidia chips in SLI mode. Single-chip cards, like the two from Nvidia in this price range, don't have that issue. We think the speed benefits of the Radeon HD 4850 X2 are worth the risks, but it's also worth noting that the possibility of a scaling issue is indeed real, particularly in the early days of a game's release.
(Shorter bars indicate better performance)
As has been the trend in other recent 3D card reviews, ATI has fallen behind Nvidia on power efficiency. It might not surprise you that a faster, dual-chip card needs more juice than comparably priced single-chip cards, but it's still worth spelling out the difference. Interestingly, the Radeon card is comparatively more efficient at load than it is at idle, but in either case, the extra performance has a real-world cost in terms of power consumption.
If this card doesn't quite deliver on power efficiency, it can actually have a direct impact on your productivity, at least if you use screen real estate as your scale. AMD has been unique in equipping certain dual-chip cards with four DVI outputs, and it's one of the features we love about the Radeon HD 4850 X2. We successfully connected four LCDs from different vendors and of different screen sizes. The card identified all of them successfully, and let us operate in either clone mode, with the same image mapped on all four screens, or in extended mode, which extends one desktop screen across every display.
Perhaps counterintuitively, you need to turn off Crossfire mode to output to four monitors. ATI's driver software makes that easy, though, as it also gives you relatively robust controls for arranging the displays in whatever order you want, and also adjusting each display's settings. Adding four displays doesn't necessarily mean you can all of a sudden play a game at 7,680x1,200, as most games will only scale to preset resolutions, and/or require specific code to support multiple monitors. You can, however, put a game on one screen and a Web-based map and a walkthrough on the others. And of course the idea of showing a spreadsheet, e-mail, and multiple Web pages at the same time will make many office functionaries drool. With each port dual-link DVI enabled, in theory you should be able to connect four 30-inch LCDs to one Radeon HD 4850 X2. We weren't able to test four 30-inchers, but we were pleased with the experience of connecting the 24-inch, 22-inch, and pair of 19-inch displays we had on hand.
Finally, as a member of AMD's Radeon HD 4000-series, this card has all of the DirectX 10.1, stream processing, and Havok Physics acceleration inherent to all the chips in that family. When we actually see those features have a widespread software impact, we'll be sure to write about them.
Test bed configuration
Windows Vista Ultimate SP1 64-bit; 3.2GHz Intel Core i7 965; Intel X58 chipset; 4GB 1,066MHz DDR3 SDRAM; 150GB 10,000rpm Western Digital Raptor hard drive