In a majority of the benchmarks -- including those with anti-aliasing and anisotropic filtering -- the ATI Radeon HD 4870 X2 was within frames of the dual Radeon HD 4870 CrossFire configuration. However, in some tests such as running Enemy Territory: Quake Wars at 2560 x 1600, the R700 had fallen about eight frames behind, or about 6%. The Radeon HD 4870 X2 isn't quite as far as two Radeon HD 4870 512MB graphics cards linked together via CrossFire, but it's darn close.
Using the Catalyst 8.8 Linux driver, we had experienced no fundamental problems with this dual GPU graphics card on Ubuntu Linux. The dual monitor support and OverDrive 5 also work with this graphics card on Linux. Through the aticonfig-based options for overclocking, we were able to increase the memory frequency to 960MHz and the graphics processor while the GPUs could only be pushed about 15MHz further, but this effort resulted in a few more frames per second in some tests. Below are the thermal results for this GPU as it was running through Enemy Territory: Quake War at 2560 x 1600 with 8x AA and 16x AF.
Running around 70°C, the Radeon HD 4870 X2 is a bit toasty, but still within its operational range.
The VisionTek Radeon HD 4870 X2 2GB graphics card is currently retailing for about $560 USD, which is about $120 more than NVIDIA's current flagship single-GPU GeForce GTX 280 and about $20 less than buying two Radeon HD 4870 graphics cards individually.
If you are after CrossFire on Linux, the Radeon HD 4870 X2 is a good candidate considering its lower price point than buying two Radeon HD 4870 graphics cards individually, but two Radeon HD 4870 X2 graphics cards cannot be combined on Linux for running in a four-GPU CrossFireX configuration. When it comes to open-source support, the Radeon HD 4870 X2 is supported by both the xf86-video-ati and xf86-video-radeonhd drivers when it comes to mode-setting, but there is currently no open-source 3D acceleration for the R600/700 series quite yet (though Coming Soon: AMD R600 3D Documentation). When there is the support though, it will be limited to one GPU. We wouldn't expect to see CrossFire before 2010, so if you intend to be using any open-source ATI driver at least partially, you will be better off using a graphics card with a single GPU.
Right now the CrossFire Linux support is limited to three titles (Doom 3, Quake 4, and Enemy Territory: Quake Wars) and the setup/configuration process of this multi-GPU support isn't trivial for the new Linux user, but we expect the configuration process to improve with time through the AMD Catalyst Control Center as well as more OpenGL titles being supported by this multi-GPU technology. If you're a dedicated gamer that enjoys playing any of the id Software titles at very high resolutions and with all of the image quality settings maxed out, the Radeon HD 4870 X2 is a graphics card worth considering.
For pricing and other reviews on ATI graphics cards, visit TestFreaks.com.