Semi-accurate are saying a few partners have samples and they saying they are at about 5850 speeds already.
Yup, its a bit of a waste to take the die size hit of a 256bit bus, without the hardware to use it.
So its shaping up like the 6770 will replace the 5830/5850 , maybe closer to the later in speed, potentially saving on die size by dropping some of the "this 40nm process is so crap we had to add stuff" waste, and increased efficiency in the uncore/shader dropping size slightly so they can sell it I would guess, around £160-170 in the uk for 5850 performance and potentially a decent wedge ahead in certain situations.
Min fps should be up as worst case scenario on a 5 way shader if each shader can only do one instruction, you only have 320 instructions on a 5870, with a 4 way shader, assuming the same 1600 shader count, the worst case scenario becomes 400 instructions, but also when something complex was to be done, the best case and worst case was 320 instructions because only one of the 5 could do complex things. So best case scenario for complex instructions goes from 320, up to 1600, a 5 times improvement(that would almost never been seen, but 2-3 when needed could make a big difference), and 320 to 400 for simple instructions is still 25% better.
The 6870 and co, well, we'll have to see, fast enough gddr5, with the speed improvement should stop any need for a bigger bus, memory is going up like 30%-ish in speed which will be a huge bandwidth increase.
The biggest increase will be on the 6770 as they are basically changing the market for it. Not sure if the 6670 is becoming the old 5770 or not, there were rumours a while back about keeping it because its a fantastic core in terms of size/yield/cost to AMD. But I'm sure an improved version would make sense.
The 5xxx series isn't spread out very well as it is, 80 shader, 5570/5670 and all the other varients of those two all having 400 shaders, an 800 shader card, and a 1600 shader card.
It looks like the next cards will be something along the lines of 2000, 1400, 800, 400, and we'll see if they bump up the bottom end cards to 100-200 shaders somewhere. A much more even spread, this gen between £120-200, theres nothing to sit right in the middle, the 5830 is expensive to make, high power and doesn't really work in that hole, you really want a card designed to be there, high yield, not selling expensive cores for cheap.
Problem is, that hole was the only reason the 460gtx was successful, if they plug it, with better cards, Nvidia has a huge core, thats slower than a MUCH smaller core. Remember the 460gtx is much slower than a smaller core already, 460gtx 1gb vs 5870, no contest, the 5870 is around 12% smaller. If they replace the 5850 with a core a further 15-20% smaller than the current Cypress and potentially even have better performance, Nvidia are screwed across the entire range, till probably Q3 next year.