Let's talk about DX11 in its current state.
For example, in BF:BC2, DX10 and DX11 are the same: "
BC2 uses DirectX 11, but according to
this interview, DX11 is mainly used to speed up soft shadow filtering. The DirectX 10 rendering path produces the same images." - techreport
Crysis isn't DX11 and still smokes 5870 and GTX480. Even without DX11, this game requires serious horsepower and looks better than almost everything else out there. This and Warhead is where GTX480 should have been 20% faster than 5870 but it just isn't for some reason.
IIRC, in Dirt 2 all you get is tessellation of the water puddles on the track so they behave more realistically and sprinkled character details in the crowd. For these small visual differences 5xxx series gets massively penalized (see 5770 and 5850) compared to GTX275 and 4890 in a very similar DX10 mode:
http://www.xbitlabs.com/articles/video/display/radeon-hd5830_11.html#sect1
At this point hardly anyone will accept that kind of a performance for only better water effects. Speaking of water effects, this isn't like comparing the difference in water Half-Life 2 with DX8 vs. DX9 paths:
http://www.anandtech.com/show/1549/2 This better not be the direction of DX11 games.
The only game that takes DX11 to a new level is Metro 2033; but enable Tessallation and DoF and it's game over for current DX11 cards.
DX11 is meant for next gen cards, just like DX9 was meant for 2nd generation DX9 cards and DX10 was meant for 2nd generation DX10 cards.
I think this fall is going to be very sad when Crysis 2 comes out and these $400-500 videocard will cry. Everyone will wish for HD6xxx and GTX5xx ()