http://astrosurf.com/buil/eos40d/test.htm
Its looking interesting. I quote:
An important difference between the 40D and the 350D/400D (but also 20D, 30D) is the adoption of the 14 bits coding. These 14 bits are really observed on the decoded 40D RAW. This performance very close approaches that met in astronomical CCD cameras. It is an essential advance, the 40D is now a precision instrument, in particular for stellar photometry'