Why would you want to buy the 24-70 f/4 when you can buy the 24-105 f/4 and have a little more range? My 105 is super sharp. I understand if you wanted f/2.8 then you'd go with that model and focal range.
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It is slightly sharper, slightly lighter (70 g), slightly smaller (0.5" in length, same width), has a much shorter MFD (7.9" MFD compared to 17.7" for the 105), is near macro (0.7x) and if you own a 70-200 or 70-300 lens, you already have the 70-105 mm range covered. But my biggest concern is how much longer the 24-105 is going to be available (just idle concern on my behalf).
That said, if I were buying today, I'd get the 24-105 f/4 IS.