John A , Apr 22, 2011; 09:51 a.m.
Well, you will probably see more flaws on the 5dII because the file is going to be a lot larger at 100%. About 60 inches wide @100dpi vs about 40 inches wide with the D700. That will show up more flaws with either lens.
I have both lenses and although I don't use the 17-40 as much, my tests and practical uses of each lens gives me the overall impression that they are very close in quality. Certain things are different, but generally I don't know that they are much different.
That said, I don't think either lens is suitable for certain things--or in every case. The corners are soft and unusable, IMO, on an FF camera for something like most landscape work. The curved focal plane just doesn't render flat fields very well (or near far). On the other hand, I have been surprised how sharp the lenses can be if the terrain is somewhat uneven and works with that curved field (couldn't tell you I am confident when it would or wouldn't work though).
The Nikon lens might in fact be better, I don't know. But if I was going to spend the money on getting a 16-35, I would probably put it towards the Zeiss 21mm which is tack sharp edge to edge--but manual focus.