Ian, thanks for the comparison. I am surprised that the image quality of the 7-14 is not better than this. I had a more detailed look at the 9-18 and find it ok, but there is room for improvement. If you look here:
there is definite corner softness even at f8, which I found gives the sharpest results at my L1. The overall contrast and sharpness is ok, but compared to the Nikon lens (and camera, of course), it's definitely not state-of-the-art. Can you confirm this for your lens? Especially the left side of the image is poorer than the right side.
In comparison with the Nikon lens I'd expect the 7-14 to give similar results.