Thanks Colin, very enlightening. I had not realised this and since my only reason to buy a xD model would be the promise of less noise at high ISO you have potentially saved me a lot of money in the future. For my purposes the 40D or the 50D will indeed be more than adequate. All I have to do now is persuade WireVixen that we can afford a car each for the girls, a special holiday for our diamond wedding, send the youngest daughter to university and splash out for a 50D .. I think we may have to go for a used Jag next year. I wonder if WireVixen will accept an X type rather than a S type.....after all the you do get the same amount of noise... in-camera noise-reduction doesn't do a lot for RAW files - it's mostly just applied to JPEG images. In Yan's case the image was shot RAW at 800 ISO - which is perfectly OK, but, noise levels are starting to creep up. And if there's any degree of under-exposure then it quickly becomes more like an ISO 1600 image (or worse).
So in reality, there's not a lot of difference in RAW file noise between cameras like the 1Ds3, 5D2, 40D, 50D etc; I put all of these in the "more than adequate" category.
Steve