We caught a rumour from Asia, that AMD's DirectX 11 chip for the performance segment, awaited in the next weeks, bets on a 384 Bit memory interface, just as the G80 did.
This could indeed be possible, concerning that the RV770 is already quite dependent on bandwidth and the RV870 is expected to have twice the computing power. Also the recent information that the chip would be bigger than 300 mm², affirms the theory of 384 Bit memory interface, because already the dimensions of the RV770 would have made it impossible there.
The source confirmed, that a pre-launch would be held on September 10. Pre-launch could also mean that there will not be any cards yet, as we heard from several sources. This is affirmed by the price which is not yet determined, but expected to be between 249 and 399 US dollar.
Because of the shortly upcoming launch it is hardly due that AMD will use GDDR5 memory on their top cards, which runs faster than 1.25 GHz. So it would be possible to reach a maximum of 240 GB/s memory bandwidth with the 384 Bit memory interface, more than twice as much as the HD 4870 would reach.