I thought I'd try Auto ISO this evening at Polish Folk Dancers' performance, but discovered that it only goes up to ISO800 on the D200 and the D2X. If the stage is lit like it was 2 yrs ago, I may very well need higher than that at this rather poorly lit amphitheater. I want to lock in my shutter speed at 1/250th, and have an open f2.8 aperture with my 70-200VR. Why does it stop at 800? Thoughts, suggestions?