No need to apologize, Mark, you're doing great.


Both are tested on an 8 MP camera (the 350D) at Photozone:


http://www.photozone.de/canon-eos/188-canon-ef-24-105mm-f4-usm-l-is-lab-test-report--review?start=1


http://www.photozone.de/canon-eos/178-canon-ef-s-17-55mm-f28-usm-is-test-report--review?start=1


For resolution/contrast on a 8 MP camera, they are similar:


1728 LW/PH MTF-50 for the 24-105 at 24mm f/4 border


1758 LW/PH MTF-50 for the 17-55 at 24mm f/4 border


1972 LW/PH MTF-50 for the 24-105 at 24mm f/4 center


2134 LW/PH MTF-50 for the 17-55 at 24mm f/4 center


(I think the difference would be more pronounced on a 15 MP body, but I haven't seen any direct comparisons yet.)


For chromatic aberration:


1.55 for 24-105 at 24mm f/4 border


0.73 for the 17-55 at 24mm f/4 border


Vignetting:


0.37 for the 24-105 at 24mm f/4 (first win for the 24-105)


0.43 for the 17-55 at 24mm f/4


Distortion:


0.32% for the 17-55 at 24mm


0.61% for the 24-105 at 24mm