I seen someone post this who apparently went to the event:

AMD says that their next-gen GPU will 250% faster than the one introduced in Jul of 2008
http://translate.google.co.uk/transl...3Doff%26sa%3DG

Quote Originally Posted by Wiki
The Radeon HD 4850 was announced on June 19, 2008 while the Radeon HD 4870 was announced on June 25, 2008
250%? Of the 4870?

Well, with 1600 shaders (double of the 4870) and faster memory at the clockspeed of the 4890 then yeah, 250% of the 4870 seams feasible.
Twice as fast and then a bit ..matches the leaked specs