I thought I mention it has the least at 16mm ? I tried it against a flat wall in my home at roughly 1~2 meters away. It does shows slightly. I understand that vignetting occurs different amount depending on the source light strength and angle at it is coming from. Generally it doesn't show up much in nature sceneries. Using your example, I can't say it's the best approach to decide on vignetting amount. You need a flat wall to determine.
Unless its really a choice of cost and you already have one and not willing to sell it away at a heavy lost, I see it pretty pointless to get one for a FX body. I have also have my fair share in getting 3rd party lenses, and seriously I stop getting them for a reason that the price depreciate much faster than Nikon lens. But then after all these while, I don't change my gear much and pretty satisfied with what I have, I see it as lower priority in this aspect. Next is I own a copy of DxO and they largely just perform correction for Nikon Lens + Body combination as their priority. That's also why I got a S95 instead of other similar brands, should I neglect the fact that S95 build is small and rugged.
Jokingly, I'm also interested to poison TS to get the Nikon 14-24 f/2.8 because it will blow his expectation away and also at the same time his wallet. :bsmilie: