I have been really busy with school and sure do want to start shooting again! I have a Canon 15-85mm attached to my 50D most of the time, but I find it too slow in low light. I do have a Sigma 30mm f/1.4 prime. Do you guys think I should sell the 15-85 for the new Sigma 17-50? I don't really mind losing out on the longer zoom range. I typically shoot portraits, random stuff, and sometimes cars. What do you guys think?