anyway, here's what David Kilpatrick has to say about Sony's noise at higher ISO:
Originally Posted by David KilpatrickI've compared Nikon and Sony models in low light with high ISO several times - most of the time, the Sony camera will give one full step less exposure than the Nikon. Not only that, but the Nikon uses a tone curve which crushes the deep shadows to black and compressed the rest of the range closer to linear - removing loads of apparent noise in the process (black level clipping). The combination of clipping the black and increasing exposure transforms a high ISO shot.
In ACR, you can try the effect - take a normal (dark) ISO 3200 shot on an A700 or A900, and set the black level slider to 0 and the tone curve to Medium Contrast. The shadows, where noise is most visible, will look very bad. Now increase the exposure by +1 but clip the black level to 10 (the default is 5) and set the tone curve to Linear.
What I found was that if I used the default Nikon D3X tone curve with the Sony A900 in Iridient RawDeveloper (one of the few programs which allows such a switch of 'hidden' processing parameters), then increased the Sony exposure to match the Nikon, the A900 high ISO really was much the same the Nikon high ISO - far better than any default result. So, it is not an inevitable fault of the camera, more a badly chosen combination of in-camera and external processing parameters which makes Sony high ISO worse than it needs to be.