I'm looking for a sharp, reasonably fast telephoto zoom. I want to be able to reach around the 200mm mark, so I've been looking at 70-200mm lenses at the moment. Lowlight performance is a plus if not a must, as I would like to get out and take some nightlife photography once I get a decent flash. But it's main use will be candid street photography and local wildlife (i.e. birds, reptiles, rodents) on bush-walks and in rain-forests. Currently looking at the Canon 70-200mm EF f/4L IS USM and the Sigma 70-200 f2.8 APO EX DG OS HSM. It really comes down to what is the better value. The image stabilization on the Canon and claimed image quality superiority or the wide aperture of the Sigma. Are there any other high performance, good value lenses I've missed? Obviously I'd like the Canon 70-200 f/2.8 with IS, but, at $3000 it's a little out of my price range. AU$2000 is my absolute maximum. Thanks in advance.