Boeing state that the increase in takeoff distance is "negligable"
Mr. Boeing is right. Rolling vs static TO difference is way down in the "noise" of performance data.
Other examples of this data noise:
Gusty wind
Variations in runway slope
Assymetrical thrust set
It's a science, but not all the unknowns can really be quantified.
(And there's a decreased risk of FOD using rolling TO technique...)