About 1Ds Mk2 / 1D Mk4 comparison: Is it all about noise? IQ is not equal to signal-to-noise ratio!
No, it's certainly not. While I know you can't really boil a sensor down to a single metric, the DxOMark overall scores are equal for the two. In fact, the 1DsII actually fares a little better than the 1DIV for ISO noise performance based on DxOMark. But my point was that the overall IQ of those two cameras is pretty similar, which is an impressive feat of technology considering that the 1DIV has smaller pixels in a smaller sensor.
Well.. I'm not all that impressed. More impressed by what Sony has done to their sensors and/or Nikon to their software: Compare the D80 and the D7000 for noise/IQ at ISO 3200 & get scared.