The steepest grade is not necessarily the hardest pull, and using the profiles to determine it can be misleading. Railroads always figured what we called a compensated grade, which figured in the retarding force of curves on the grade. This, of course, was also affected by train lengths.
As a rule of thumb, we added 1 ton to the tonnage of a train for each car in a curve (at any given time) times the degree of curvature to come up with a compensated figure. / Ron