Do you see a detail difference between these two? They were shot with the same aperture diameter.
What did you shoot the second image with... and what settings?
First image is with a 20D @ 280mm, f/6.3, 1/200s, ISO400
Second image is with a T2i @ 560mm, f/11, 1/20s, ISO200
I wouldn't count on the EXIF data as the teleconverter stacks were different and only the first one reports.