http://www.firingsquad.com/hardware/hdr_aa_ati_radeon_x1k/
And their conclusion? HDR + AA is a useful and completely playable feature. From the article, adding 4xAA/8xAF to FarCry (HDR on) at 1600x1200 produced a FPS hit of 4% and 2% for the X1900XTX and X1800XT, respectively.
Adding 4xAA/8xAF to Oblivion (HDR on) caused a drop in framerate of 30% and 21% for the X1900XTX and X1800XT, respectively.
And their conclusion? HDR + AA is a useful and completely playable feature. From the article, adding 4xAA/8xAF to FarCry (HDR on) at 1600x1200 produced a FPS hit of 4% and 2% for the X1900XTX and X1800XT, respectively.
Adding 4xAA/8xAF to Oblivion (HDR on) caused a drop in framerate of 30% and 21% for the X1900XTX and X1800XT, respectively.