I am no insider, nor I have any inside sources, but I think people are over optimistic about 6970. Nvidia 580 can acquire 20% increase + lower power consumption over 480 is because a)it has one more SM, and b)tweak. Although the process is the same 40nm, it actually have 10.67% more working parts in comparison. In other words, 580 is a fully working chip where 480 isn't. Now look at 5870, it is a fully working chip to begin with, 6970 will have a harder time bumping up the performance in comparison.
So 6850 has 960 SPs, 6870 has 1120 SPs, my guess of 6970 will have 1200-1300 SPs. Let say it scales really well + tweak, it should be no more than 20% over 6870, which will be roughly at 480 level. Assuming that it is power efficient, than it is a card with 480 performance, 5870 power consumption.
Try to clock it means giving up power consumption, if they can't clock it up to pair with 580, then they actually have no selling point. Also, Richard was upset about high level tessellation, indicating that 6970 isn't going to beat 480 on heavy tessellated scenarios. Having said all that, it can be priced at around 300-350 as a powerful card that have better performance/watt ratio.
Look at 580 for a second. Nvidia is brave enough to put a limit on OC on benchmarks. It appears that they are pretty sure about its performance over its competitors. 480 isn't the greatest build and it is very hot, yet Nvidia didn't put things like that on it, so why now? What is more dangerous? Having user kill their card during OC or having their competitor win and crazy fanboy nerds can't do anything about it?
Now I don't know how many SPs are there, so I can be very off. (OMFG 2000SPs!!)