Hi, just seeking advice. I have a 17-55 2.8 Nikon lense which I'm currently using on a D700 body, while I use a 70-200 Nikon lense on a D3S. I use both bodies with each lense mostly for low-light theatre photography. I had initially used the 17-55 on a D300, but have since upgraded without changing lenses. The 17-55 delivers very sharp images on the D700 (in FX mode, without DX cropping), and clients have been happy with the results. I've been using this combo for photography work for the last year, though I've started to look into buying the 24-70 Nikon lense after reading posts and reviews that it's a better lense for the FX body. From what I've seen of the selling prices of the 17-55 on Ebay, if I sell the 17-55 lense, it will cost about an extra $400-500 to purchase the 24-70. My question is whether the curvature and barrel distortion that I've noticed in the 17-55 at the wide end on the FX bodies is still present in the wide end of the 24-70 lense on an FX body, and if there is much noticeable difference in image quality between the two lenses? The 17-55 has usually been sharp enough in focus for my needs, and I've been able to take care of the vignetting in Lightroom 3. Generally, have others found the 24-70 to be a step up from the 17-55? I know that it goes without saying that an FX lense is better suited to an FX body, but just wishing to hear from photographers who have used both the 17-55 and the 24-70 whether an 'upgrade' or change-over from 17-55 to the 24-70 for use on a D700/D3S will be worth the extra dollars? I'm also concerned about the number of forum posts which mention faulty zoom ring problems on the 24-70, necessitating returning the lense to Nikon for mechanical repairs under warranty, and I am unsure if this is a common issue with the 24-70? Many thanks.