That's the million dollar question to be answered this Thursday, and what performance do we get for that price, compared to nVidia's GTX-285 and 295 ?
I'll say this right now. I don't expect nvidia's last gen to be competitive with ATI's next gen on price. I think the million dollar question will be in 2 or 3 months when Nvida's parts hit the shelves to see where the price/preformance lies then. It'll be a speed bump for Nvidia if they are priced wrong for 2 months, it will be a disaster for ATI if they are uncompetitive after Nvidia releases it's cards.
If the 380 is x2 a 280 and the 5870 is the rumored 1.6X the 4890, that would make a 395 25% faster than a 5870x2. Which means it would be price/preformance equal at 750$. If Nvidia releases the 395 at 600$, that would mean the 5870x2 would need to drop to 480$ to be competitive.
Of course, who knows where (or if) Nvidia will come in, or where the 5870 will come in on preformance. Hopefully we'll get one peice of the puzzle soon enough.