Sigma 17-50 2.8 vs 17-70 2.8-4 ?

Does anyone have experience with both of these lenses? If you considered both, why did you choose one over the other? I've been considering the 17-50 for the constant 2.8 but started wondering about the extra focal length offered by the 17-70. I'm thinking that if I get one of these two lenses, it might be on my D7000 more than my 18-105. Thanks.

No direct experience with either lens, but the instructor for a few college photography classes here locally swears by his Sigma 17-50mm/f2.8 fixed aperture. He does shoot a lot indoor thought (weddings, interiors, etc), but he gets good results.