Spending that kinda money for the Sigma 24-70mm when you have the DA 12-24mm is pointless imo. I find the most versatile range is about 17-70mm and to me if there is some focal length overlap with the DA 12-24 so be it. If you're open to a suggestion, use the DA 12-24 and pair it with the Sigma 30mm f/1.4 prime. There is a nice transition in focal range plus you get a fast prime that works well for available light shooting. If you need a short tele, get the DA70.