The good news is that images look really great at ISO6400.
Color is nice, noise is barely noticeable. I did use some flashes this time to supplement the light coming from the window and the venue's brown lights. The lights were set to 1/16 or 1/32 so as to blend well with the ambience.
That said, as soon I went over 6400 ISO, photos were visibly degraded. Color was smudged and brownish. Also, the pixel count does not really matter at that point. I wish the camera would just decrease the number of pixels at that point, to save on disk space.
There are some good news though. The photos would look better in high ISO if the light is between 3200K and 5600K. It will look better if the contrast is good. Also, if you left the high ISO on by mistake, as in the A99 in a lot of cases the photo will NOT be overexposed. The camera will figure out that it has enough light for the pixels and will compensate.