Radeon HD 4870 X2 was a monster as shown by the many reviews posted so far, ours is still in the works. With its two RV770 GPUs clocked at 750MHz and memory chips operating at 900MHz (3600MHz really) it has reclaimed the long lost performance title from NVIDIA. The real kick in the teeth for NVIDIA is that the card is actually profitable for AMD, with a margin, but the thing is that there is still one more blow to come. Radeon HD 4850 X2 is not yet available, but should arrive in stores later next month.
The biggest technological difference between Radeon HD 4870 X2 and Radeon HD 4850 X2 is the memory type. The former uses bleeding edge GDDR5 memory circuits, while the latter uses GDDR3. This means that it will have about half the bandwidth, which will limit performance somewhat. It also has a lower core frequency, 625MHz vs. 750MHz, which makes up the biggest performance difference between the two. However, there is always the option of overclocking.
Performance is expected to be slightly lower than 4870 X2, but still very competitive with NVIDIA’s enthusiast cards of the GeForce GTX series. Right now it looks like Radeon HD 4850 X2 will be priced to compete with GeForce GTX 260, while performance should be a notch or two higher. One more month to go before the card surfaces.