Midrange zoom for DSLR video

I'm using a D7000/Nauticam system for both stills and video. I've been using the Nikon 12-24mm as a midrange zoom. Although it's an excellent big critter lens, the soft corners won't work for video. So I'm looking at the Sigma 17-70mm. Does anybody have experience with this lens shooting video? At which range are the corners sharp, and what sort, if any, diopters do you use? Any other lens recommendations for DSLR video? (I'm also using the Tokina 10-17, Nikon 60mm macro, and Nikon 105mm macro)

I've always had good results using a +4 diopter with the 12-24mm when shooting stills of medium to large subjects with my D300.