I'm usually ok making decisions about gear I want or need, and normally just ask for user opinions on certain gear or alternatives I may have overlooked. This one is different. I have a sigma 18-35mm f1.8 (underused but great). I decided to trade this and buy a sigma 17-50mm OS f2.8 because I think it would get more use and be a better walkaround lens. The price I was offered on trade was very poor so I put it on a local site but no real interest. I used it last night in a tight enviroment with only ok light and it was great, so I'll probably keep it. Do you think its a waste to still purchase the 17-50 because of the overlap.