I am in the frigid mountains for some early winter shooting (12° F today at 10,600') with both the new Zeiss 25mm f/2 Distagon and the new Leica 21mm 3.4 Super-Elmar-M ASPH. I write this using the AT&T personal hot spot on my iPhone 4S, high in the White Mountains of California.
The Zeiss 25/2 Distagon offers extraordindary contrast for coarse and medium structures, for a visual impact that can scarcely be rivaled, though the 25/2.8 Distagon has similar qualities at one stop slower and with some color aberrations. The 25/2 Distagon has a purity of color that is truly extraordinary. Which is not to say that one won’t find some lab test purporting to show that lens X is just as sharp— which could be true, but beside the point, if one looks at real images.