I have a A300, ACR 5.1 and Elements 6.0 I have recently compared three raw plugins, Adobe ACR, Sony's image convertor and Silkypix free. With the Sony s/w I turned off all automatic processing. The results are a surprise.
The same raw file has much more noise when being opened in ACR and requires a great deal of exposure reduction to reduce highlights and get the highlight warning to disappear from within the plugin.
When saved as jpegs from the various covertors the ACR is noiser and all settings seem too strong. On very noisey photos (or at least photo that look noisey from within ACR) it some times isn't possible to clean up the noise. It just doesn't seem ACR is doing a propper job of opening the Sony raw files.
I do like the ACR plugin and it is much quicker than the Sony but at the moment there does a ppear to be a quality loss using it.