By the way DxOMark, the Canon f2 IS USM lens is shown in the sharpness field map results as being measured at f1.4 although the accompanying text does relate to f2 -needs a small edit.
My conclusion from the sharpness test is that the top three lenses all have about the same sharpness at f4. The only material difference is how they fare at wider apertures. Could this not be used to advantage though? If one had a small subject in the centre of the image and wanted to isolate it from the background using f1.4, wouldn't the Zeiss come out on top as all else in the frame would not only be out of focus but also unsharp? Is sharp bokeh better or worse than unsharp bokeh?! If knowing the characteristics of the lens thanks to DxOMark, doesn't the Zeiss offer more creative options?