I am in the market for a 24-70mm f2.8 lens and a 70-20mm f2.8. I have used Nikon's lenses in the past. Great quality, sharp images. The Nikon versions of these lenses are excellent, yet very expensive. I have been reading about the Sigma versions and I'm interested in anyone's experiences with these lenes. In particular I'm looking at the newer versions of the lenses.