FUD Zilla heard the actual launch date of the ATI Radeon HD 4890 is April 9th and not April 6th. The latter date had been floating the web because of a misinterpreted statement from AMD, they said "week of April 6th" and some people wrongly took this date as the launch date.
Additionally, the rumor site also claims to have seen the final specifications of the card. The ATI Radeon HD 4890 reportedly has a 850MHz core with GDDR5 memory clocked at 3900MHz. Besides higher clockspeeds, the card should also have slightly more efficient shaders to up the performance some more.
You can expect the card around April 9 for roughly 250EUR.