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I can't see a dual 6970 based card being much more viable than a dual 580 or dual 570 - they are only ~18% less power hungry than the 580s and less than 2% cooler running - sure with 2 cards that quite a saving but they are still well above the envelope for a dual card - at best it will be a hugely underclocked pair of cores.
Given the respective TDPs its not going to be hugely different.

Not hugely in that it would be between 200-400 watts above the ATI card![]()
Are these consumption figures peak or typical?
6970 is rated as typically 190W and 580 as 244W I believe.
Min. PSU recommended for 6970 is 550W, for 580 its 600W.
Edit, says 550W for 6970 on AMD site and 500W for 6950.
Considering Anandtech(who are in themselves completely stupid, http://www.anandtech.com/show/4061/amds-radeon-hd-6970-radeon-hd-6950/24 ) show a 49W difference in Crysis and a 130W in Furmark without the 580gtx furmark limit removed.
Basically at "default settings" for both cards, IE no power applications changed, the 6970 will not use more than circa 200W, just below mostly, the 580gtx will use up to 300W.
The ONLY time they come close is when some website uses any uber high loading benchmark or furmark, removes the limit ONLY on the AMD card, and then compares to a 580gtx, even then the 580gtx comes out using more power.
In realistic situations the 6970 uses quite a lot less power, and it has more memory on board which makes another 5-10W of difference aswell.
As for cards, why do people consistantly across loads of forums suggest full cores won't get used in these cards as its a waste.
for X performance figure, whatever performance target they want, more cores and a lower clock and voltage will always, always use less power.
Why did the 295gtx use 240shader cores and reduce other more power hungry aspects of the card like bus, because a 216 shader core would need increased clocks and increased stock voltage to hit the same performance level, which would have used more power.
Almost every dual gpu card ever made uses ALL the cores it can at as low clocks as it can, because its the single best way, the ONLY option for the lowest power usage possible.
You either have, as an example, with a 580gtx, 2x512 cores, at 1.0v at 550Mhz, or 2x480 cores at 1.05v and 605Mhz, both will offer the same performance, the former option will use less power.
Any dual Nvidia card, if it comes is almost certain to be a 2x512sp gf110 based card, or a 2x384sp gf114 based card. Likewise Antilles will be either 2x1536 Cayman shaders, or 2x 1120 cypress shaders(2x6870's).
Rroff its worth noting that the only people that claimed there wasa dual gf110 card coming, insisted BEYOND a doubt it would be out BEFORE Xmas, and they insisted this for 2 months straight, untill there was a week left then all of a sudden they started insisting it was delayed for no apparent reason as it was completely ready.
As for 2x580gtx's using at max 100W more, aside from not a single review I've seen agreeing with that, you fail to see the problem, if the 6990 uses 299W, then 100W more would put the Nvidia duallie at 399W, or, something they wouldn't make, 3rd party silly low volume special edition cards, sure, not many people really care about the 300W limit, except those that break standards and those who want to sell a card in high volume. IE Nvidia, AMD, Dell, Hp, etc, care about the 300W, and no one else gives a monkeys.
EVGA have long been a "release something ridiculous we can't release ourselves as we'll look mental" backdoor product launch company for Nvidia, but even so the EVGA leaked shots still look likt gf114 cards.
Anyway, who cares, I mean really, AMD dual high end cards offer good value(in general) but who can't build a system to just take 2 cards with improved cooling and overclocking anyway, theres little compelling reason to buy a dual gpu single pcb card at all.