Ok, I've caught something. Is there a bug between AA and no AA when using DX10? Look at the results using DX10. AA has higher score then without AA.
Dunno, I did check my screenshots and its ok, I didnt look at the uploaded picures because I cant get to open Imageshack this morning.
DX10 @ 1280x1024
NoAA - 160.50 - 122.89 - 202.01 - 130.30
4xAA - 143.10 - 97.93 - 185.24 - 114.94
8xAA - 141.21 - 95.71 - 176.47 - 109.74 (CAT 8.5)
DX10 @ 1680x1050
NoAA - 135.03 - 102.59 - 169.64 - 109.52
4xAA - 115.94 - 85.54 - 138.42 - 98.83
8xAA - 106.09 - 73.31 - 117.05 - 85.45 (CAT 8.5)
EDIT:
DX9 performance i think is a driver issue, last NV drivers are getting bad results in DX10, this new driver 177.93 gave it a boost in DX10 mode. I believe is the same with ATI, DX10 is working better then DX9.
And if you mean DX8 not taking so much hit from DX4, thats normal when the game works fine with a X2, same happens in Crysis, enabling AA give a % hit in performance, but after that it doenst matter to much if you are going to use 4xAA or 16xAA the performance hit its almost the same.