Is the 14-30 not going to be a great night sky lens because it's f4? I'm not an astrophotographer myself, so I don't really know whether fast lenses are preferred. I can see the star trail issue with a slower lens, but I'd think there would be a depth of field issue with a really wide aperture if you had anything in the foreground (a sky-only shot is by definition entirely at infinity). The 14-30 is going to be very sharp at 20mm from what little we've seen.
Dan