Supposedly DX11 plays well with ATIs arch, meaning that how they already have done things its to their advantage, add in the other structural additions from this gen, and the rumored performance , and Ive heard this in several places, and its only rumor, is between a 4870x2 and a 295 for the 5870 or whatever theyre going to call it, and it isnt the top card.
Doing nothing, or using the old arch, we can see up to 40% more in an optimised game, add in the arch changes, and yes, it could be actually double perf, thats best case, but not bad. Of course having up to twice the available power wont go to waste, as the devs will crank up tessellation, AO and a few other things, but this is what DX11 was for, not just to have AO done better, or bring tessellation in, but to make your gfx cards work better, on an easier SW platform for dev ease, with fewer HW fixed functions, meaning let the CS (compute shader) do the heavy lifting, being unified to do more. Its the very construct of each companies compute shader that may have an advantage here, and it appears since CS has a wider use, those 4+1 we see in ATI sees a bump from CS, where its the same, or a tad detrimental in the nV shader setup, which will have more gains in other ways, more leaning towards DP and GPGPU usage, which is good in its own way as well