The board partners want to remain anonymous of course and thus we can't guarantee that the following details are one hundred percent correct.
Based on the information we received during our conversations it seems like the Ati Radeon HD 4890 (Single) will compete against the Geforce GTX 260 and not the GTX 285, since it seems like for the Ati Radeon HD 4890 only the frequencies of the GPU and the memory were increased. Accordingly the calculation units aren't changed. Basis for the increased frequencies is the 55 nm production process, which has been quite perfected by now. 850 to 900 MHz appear to be possible for the RV790 GPU; the RV770 of the HD 4870 is clocked to 750 MHz. As the GDDR5 memory of the HD 4890 (Single) is regarded, AMD wants to reach 3,900 million transactions/s - RV770 based cards reach 3,600 MT/s. Those numbers indicate an increase in gaming performance of 8 to 20 percent, depending on game and sequence.
PC Games Hardware also wanted to know the odds for and against a possible Ati Radeon HD 4890 X2. From a technical point of view such a card shouldn't be a problem, but it remains to be seen if AMD will really invest time into such a prestige object. A Radeon HD 4890 X2 might hit the markets only if it can noticeably beat the Geforce GTX 295. Probably AMD will leave it up to the board partners to build such a card or they are looking for exclusive partners like they did with the HD 4850 X2 which is available from Sapphire only.
The Radeon HD 4890 is supposed to hit the markets on April 6. This date, which has been brought up by VR-Zone initially, has been secretly confirmed by the board partners. But as usual such a date can easily be rescheduled ad hoc. We were also told that the cards will cost ?230 to ?240, although it is unclear if the cards will have 1 or 2 GiByte VRAM initially.
Source: PC Games Hardware