Mike,
Just for you (
)have added a few test images made with the Sigma 17-70 of the milky way at different focal lengths:
http://www.pbase.com/terrylovejoy/sigma1770
The filename in the caption gives you the focal length followed by the focal ration (decimal point omitted). All images processed similiarly in IRIS and are 2 minute exposures at ISO400 with a standard 350D.
PS Photocontinental in Brisbane are selling them for $479 at the moment.
Terry