I'd have to agree with these points.Originally posted by sputnik
- full frame sensor
- ability to shoot at 1600/3200 ISO without noisy images... better image quality in general
- quiet shutter for shooting ceremonies without being a distraction
ISO 1600 on the 5D is about as noisy as ISO 400 on the 20D. By the time you downsize a 12.8MP image to fit inside an 8x10 print, most noise will be gone or hidden anyways. Also the first thing I instantly noticed when firing the 5D was how quieter the shutter was and how much softer the shutter button felt.
I found the colour a lot more pleasing on the 5D as well, even with both bodies custom balanced in the same lighting conditions.
Now how well the 40D compares, I couldn't say.