Heathrow Director:
"In my opinion the 17-40 beats the pants off my 24-105 L lens in terms of sharpness."
I am surprised at that as the 24-105L is highly regarded in DPReview. If anything a lot of opinion is the reverse and as a user of both I tend to agree although they are both excellent lenses. Do you think it is possible that your 24-105 autofocus may be less than it should be?
I have a 70-200 F/4 that is regarded as one of Canon's sharper lenses yet mine was quite soft at the short end. I sent it to Canon with an outline of my concern and asked them to check it and it came back more like it should have been.
I am very surprised that the difference you are getting is of the "beats the pants of" category.