Originally Posted by
PEI_3721
The description at #1 re the 737, is ‘Crossover Speed’ - not AoA. This is the speed at which full opposite roll-control cannot maintain wings level flight with full rudder application due to failure.
The more fundamental variance is with AOA, not speed. If it was just a matter of speed, then the relative effectiveness of the rudder vs. ailerons would not change, as they're always flying at the same speed.
But dihedral effect (pushing on the rudder causes a roll) for a swept wing, increases with AOA. So at high AOA (read: low speed at steady state) the rudder is more effective at rolling, and thus, may overpower the ailerons.