My experience in setting brightness when using HDMI input is that the projector can display black, the 2% pluge pattern (using DVE disk) and up to 100% white but will not display blacker than black or whiter than white levels. It does not make a difference if the auto iris is engaged or not.
Its interesting that my manual and the on line manual does not indicate the motion flow feature which is accessible in the menu. I tried using it on 1080p 24fps dvd and it made quick movements very "blocky". When the feature is disabled the motion was much smoother.
Compared to my old DLP this unit puts out a very sharp image with typical DLP 3d "pop".