I have a theory about 20nm cards from both AMD and Nvidia..
Bear with me..
I believe the performance VS power use is so much better on the new AMD/Nvidia architecture on the 20nm node, that this is the reason we are not getting any leaked information.
If they were leak info now it could cannibalize sales of things like 290X / 295X2 and GTX 780Ti / Titan.
I think we're gonna see a massive leap in performance VS power use, to the point where older cards will be irrelevant in those terms in comparison, anyone who knew would not pony up the money for a 780Ti / Titan / 290X / 295X2.
The first wave will offer 290X / 780Ti performance in a power envelope about half what we have now. A massive difference, the second wave will use more traditional power envelope but as performance is so much greater it's possible we will have Titan Z / 295X2 performance in a single chip..
Or I could be wrong lol