I remember reading somewhere (may have been on pprune) that some airline called V1 a few kts early, as had been their custom. This continued until Airbus pointed out that their published V speeds already accounted for the human factors aspect of it, and thus calling V1 early was inadvisable. Again, not entirely sure of the source. It may have been an airbus publication, or just something that was posted on a forum, but it bears consideration.