I just got back from making more test images using the Sigma DC 17-70mm lens on the SDQH body. In the original post, I said I saw no vignetting with this lens. That's not correct.
I've just looked at the tests and there is definite vignetting in the corners. Cropping these images by hand, I need to reduce the image file size by somewhere between 10 and 15 percent. If I use the Auto Crop feature of the camera, the image file size gets cropped by 30%.
So I'm debating whether to keep the lens or not. I like the image quality produced by the lens. And I definitely like the small size and weight when compared to the Sigma full-frame alternatives. I'll likely keep the lens until Sigma wakes up and starts making some small, light-weight, less-expensive prime lenses.