R/G,
I'm torn...I haven't plowed through all the links you gave me, yet.
Probably the 50, though the 40 is not slouch, but the $ diff is
negligible. Funny how the 500D has practically the same specs as the
50D, for a lot less dough. I know it's a "cheaper" body...but, these
cam mfg'rs flood the channel with a dizzying array of nearly the same
species.

Digital Cameras Side-by-Side, 3 cameras: Digital Photography Review