Fudzilla: "The new addition to the Radeon family is called HD 4890 and it is AMD's fastest single-GPU card at the moment. This card will let AMD catch up with the Geforce GTX 260 SP216, and it scores up to 10% better results than the HD 4870 1GB. Since these two cards are not any different specification-wise, the improved scores are a direct result of HD 4890's higher clocks. It runs at 850MHz, which is 100MHz more compared to HD 4870's 750MHz. GDDR5 got a boost as well and instead of 3600MHz now runs at 3900MHz.
The new card's GPU is codenamed RV790 and it packs 965 million transistors, just like the RV770 found on HD 4870/4850 cards. These two graphics cards, the HD 4870 and HD 4850 use the same GPU, and it's only the clocks that set them apart. We're currently unaware of anything that's changed for the RV790 besides optimization and increased clock speeds. There are still 800 stream processors in 10 SIMD clusters, and the 40 texture units and 16 ROPs have been left unchanged as well."