So I love the photo quality of my Canon 17-40L. It is wide enough for me (I have a Rebel XSi), but I wish that it were longer. What do you all think about trading it in for a Sigma 17-70? Any other suggestions? I have a Siggy 30mm and 50mm. Thinking of getting rid of my Canon EFS 10-22 (just too wide for most uses). I'd like to just have ONE walk around lens like the 17-40 only longer.