Thank you all, I ordered it.
Also just received the Tamron, what a fantastic lens. Still testing but first results are breath taking. This is almost as good as a prime (I mean for sharpness, not distortion). And that far, vigneting is not visible in the shots I took. I am wondering if the D800 is not increasing corner brightness anyway, even if the lens is not a Nikon.
At first, I thought VR made pictures less sharp, but this evening all seems ok. I can now take bright pictures at ISO 3200 and 1/8th or slightly less that are perfectly usable. They even look bright as if the room was brighter than by naked eye.
Last good surprise is that in Switzerland, Tamron offers a 10 year warranty, covered by Leica service center!
really feels like a great deal.