A HD7970 is on average 31% faster then an HD6970 (previous AMD top GPU), and just 12% faster then an GTX580 (current NVIDIA top GPU) at 1920x1200.
If we talk about performance per dollar, at 1200p, the GTX580 actually has an advatage, because the AMD cards have their prices very much inflated, especially in Europe, and you pay a lot more for that 12% performance advatage.
The same HD7970 is about 50% faster then the current mid-range NVIDIA GPU, the GTX560 Ti (vanilla, not the special edition 448 core) at the same 1200p resolution. I'm not going to say how much more bang for the buck you get with the GTX560 Ti because it's embarrasing for the AMD card.
This is all according to TPU.
What I'm wondering now, it's how much performance do people expect for the GK104 card priced at $300 to warrant all this distrust. What do people expect the performance of the GK104 card (GTX660, GTX760 or whatever it's name will be) to be in relation to the GTX560 Ti?
It's clear that GK104 should outperform a GTX560 Ti. Let's say it's ~30% better. Well that puts it in GTX580 territory. For almost half the price of an HD7970. All of a sudden the HD7970 costs ~100% more for just ~15% more performance.
I'm sorry, but paying double for just a bit of extra performance contradicts the AMD customer charta. This is what kept AMD alive for so long, in the CPU and GPU markets. You don't have to have the fastest CPU/GPU as long as you price it correctly to make it attractive. AMD already f@#&d that up with Bulldozer. So they're on a destructive pricing curve.
And you can adjust that 30% and downplay it to 25% or 20%. But that's not realistic. A new card should outperform it's predecesor by at least 30%. It's just how it is.
What makes it a nightmare for AMD is that this is their top GPU, their "enthusiast chip", their high-end, while GK104 is NVIDIA's "performance chip", or mid-range GPU.
So whatever you read about AMD or NVIDIA right now, apart from being a fabrication and a complete joke, is rendered nil if you just stop for a moment and think about it. Take your fanboi hat off for a minute and do some simple math. You can do some aproximations, I don't mind. Percentages in the single digits will always fall prey to erosion due to driver updates.