I think first you can review the original size photo by the 2 lens on 40D, then you will find the photo quality of the 2 lens.
40D + EF 300 f4
http://english.sellpower.net/modules..._mm=0&B1=Query
40D + EF 100-400 f4-5.6
http://english.sellpower.net/modules..._mm=0&B1=Query