Remember that the quote comes from some time ago. Modern performance calcs/capabilities can muddy the picture.
Derate is available on the 777 300 er to 40% and assumed temps of 72 degrees C are not uncommon.
Also, the optimisation of V2 can change the picture, V1 being increased to "almost" balance the field and Vr increaseing to take advantage of any spare runway length, so increasing V2 and climb performance/wt available.
So a small change in the assumed can give a relatively large change in speeds or a change in optimum flap for the same wt/runway.