How is 12-35 AF in Low Light

as I am considering this lens, one important question I have which is critical to me, for those who own that lens.   How is its AF in low light?   For example, my 45/1.8 is very fast in good light or lowest of the lights, and so is my 14/2.5.    On the other hand, my 75/1.8, although it has fast aperture, struggles often in low light on my OM-D, but does excellent in terms of AF speed in good light.   Does anyone has experience specifically with 12-35 in very low light conditions (dark clubs, discos, dark restaurants, etc, where you have to focus on people faces).  I need a perfect AF, otherwise no use for me in that $1200 lens.

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