After reading the review it is wise to go to the topic discussion forums; 50D-10D.
Consulting the many posts, you can conclude that iso and image quality wise, the 50D may not be the big expected step forward compared to the 40D, but many real users having both a 40D and 50D, favor the 50D (if only looking at performance and not taking into account the price difference and the question is it worth to spend more money for a 50D rather than a 40D).
Allthough I cann't comment for a 40D user, I changed my 30D to a 50D and I must say I'm pretty impressed about AF-speed (very important in our hobby), image quality and iso. For shooting in the high iso-range, the test is less important for me because those are not the values in which I want to shoot aircraft. Normally high iso means dark and/or bad weather.
Enclosed a fast example of a 747 while landing on EHAM. I was hesitating to post the pictures because until now I'm not able to post the same sharp pictures on the internet as I see them on my screen (I have to figure this out). Sorry. Anyway these are straight out the camera JPEG with default setting sharpness five, without post-processing. Taken with 500 iso and you can barely see any noise.
When shooting raw and postprocessing the image will even look better.
Just my 2 cents. Maybe this might help someone.
Emile