Yes, I realize the FF equivalency. This is getting off topic from the OP's original post, but I've read numerous times online that the 17-55 is sharper. I don't have a 24-105 to compare it to. However, I've never been disappointed with the performance of the 17-55. Coupled with the extra reach (my 70-300 for instance becomes a 112-480mm and faster frame rate... and no, I can't afford the 1DX's 14fps) it was enough to convince me to keep my 7D as a second camera. I now shoot with both, and they make a great combo. The similar interface and body style makes switching between the two a seamless experience.
Bottom line is that if you can't take a good picture with a crop camera, then you can't take a good picture with a full frame camera either. As far as equipment goes, they're both excellent.