Sorry, I haven't tested side-by-side but if you are mostly shooting in brighter conditions, it should not matter for focus. In very low light, my guess is that there will be a slight difference. Most of us go with the 2.8 because we need every bit of extra light we can get.
Other option, buy a monopod (which I personally hate) or take body building
Good question though, I haven't seen tests of this in lower light.
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