I'm sure when the Zeiss lens becomes available it will be razor sharp, even wide open. I just got my copy of the Nikkor 24 PC-E tonight and it's too early for me to render a full verdict on the lens, but at f/4 it's not as sharp as my Nikkor 14-24/2.8 is at the same aperture, it's not even close. On the other hand, I know this lens can do great things that I will not be able to do with any other lens, which is why I forked out a small fortune for it.
For Mark, I can say that my Nikkor 14-24/2.8 is extraordinarily sharp at all focal lengths, at every aperture, and even into the corners.