I currently have the 17-85 IS and I love the range. But I have found though that the performance at 17mm, especially around the edges, leaves some to be desired. I am seriously considering upgrading to the 24-105L, but I'm concerned about the usability on my XTi, as it would then be a 38-168. This doesn't leave much on the wide end, so I would probably also pick up the Sigma 10-20. So I'm wondering if it's worth dropping $1500 on a 2 lens combo to replace my current one lens setup. I don't do any professional shooting a the moment, just as a hobby. To those that have the 24-105 on a 1.6 crop body, do you find yourself looking for something wider as a walkaround? How much better is the 24-105 over the 17-85 really?