Wide Angle Zoom question

Hi,

I am planning to buy a wide angle zoom to cover mostly events like Birthday parties and dance events. I am reading reviews of Nikon 24-70 f/2.8 and similar offerings from Sigma and Tamron. One main reason people say Nikon is the best because of end to end sharpness with wide open. Tamron and Sigma seems to be a little soft at the end, but center sharpness seems to be good.

If I am mainly taking people pictures, who will be centered in the frame 90% of the time, will it matter if the end sharpnes is not much? There is almost one thousand dollars difference in price.
Thanks.