AMD's HD 4890 Series is a solid upgrade from the HD 4870. In our testing we see a performance increase of 13% when averaged over all benchmarks and all resolutions. Considering the core clock increase is 13.3% from the HD 4870, I see the theories confirmed that predicted the RV770 to be a clock scaling wonder.
It is sad that whoever chose the fan speed settings of the HD 4890 must have been deaf. The card is very noisy in both idle and load, despite running at comfortable temperatures. We have tested a HD 4870 to emit 32.5 dbA under load, the HD 4890 is 43.3 dbA. A 10 dbA increase is generally accepted as double the perceived fan noise. So why is the card twice as load? It's not twice as fast nor does it consume twice the power.
AMD has been working on the HD 4890 pricing until a few hours ago. The latest information we received them was that the card will cost $229 after a $20 mail in rebate. At this price the HD 4890 can't compete with the GTX 275 when it comes to performance per dollar. AMD has been praising the overclockability of their RV790, but it seems we were unlucky with the cards we received. My guess is that an aggressive binning strategy put the best overclocking ASICs on the press samples that AMD sent out.