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beware, the differences are much more than the FOV.
The 28 has definitely a different rendering: the mint copy I tried had much, much less than microcontrast wide open than the 24, and was not terribly sharp at 1.4.
Its rendering was beautiful, and delicate (again, the lack of microcontrast), with a smooth bokeh.
But, like the 28-70, it suffered from rather heavy CA wide open and at F2.
The new lenses are really a step up in pure optical terms. In any case, I regret not buying it: it is a very rare lens...