These things all have to be taken into account in the original calculation for how much power to use. It is impossible to determine the answer to that question

These things all have to be taken into account in the original calculation for how much power to use. It is impossible to determine the answer to that question without having the information necessary to calculate an expected acceleration profile for the takeoff. If you are using approximations in that calculation (such as the average weight of a passenger), then that same approximation can be used in calculating the acceleration profile, and if you are falling significantly short, then it shows that the calculation of the power setting needed for a safe takeoff is unsound in some way. That alone is sufficient to justify an abort.