A99 and sensor evolution

Downsampling removes detail, more at 6mp  than at 12mp. But you don't have the same detail with a a 6mp or 12mp camera as with a 24mp camera.

The test proves:

1. That for a similar size a99 6400 ASA is as good as a 200 ASA Minolta 7D

2. That a softer tonal curve gives smoother and les noisy transitions in the dark tones and shadows.

Noise reduction was not very high. Sharpening 100 at 0.6 and luminance nr of 35.

The following comparison at 12mp is with zero sharpening and zero luminance nr for A99 (left) and D600 (right)

Using noise ninja will not add more detail and not remove noise better. Your sample of the a900 looks horrible.

A99 left, D600 right - downsampled to 12mp, 0 sharpening and 0 luminance nr