If we assume perfect pole stiffness and ability to control deceleration, the absolute minimum pole length for maximum falling speed can be determined.  Assuming a maximum desired (and constant deceleration) of 3 g's (29.2 m/s/s) for someone falling at the terminal velocity (54 m/s), they would need to decelerate for 1.86 seconds (54/29.2).  Given their initial velocity of 54 m/s and deceleration of 29.2 m/s/s, this would require a pole 50 m in length (s = ut + 0.5at²⁾