Just as a thought, I'm a master at knowing nothing about the technical side of things, if we put a 91 against a 90 as a passenger loco then the 91 is obviously in the lead but a 90 is perfectly capable, what though if we were to compare the two as freight locos? how would a 91 perform given a couple of thousand tons to haul? if you needed an available electric loco for freight would a 91 be worth the effort?
the gearing is different.
cl90's are very quick off the blocks but not so good high end.as freight loco's they are pretty well proven workhorses,and a good cl86 replacement.
no reason why cl91 coudn't be regeared. ok lower speed but extra poles in traction motors= way extra torque.
for freight use realistically only 75mph/90mph operation required.
they can pull 500t at 140mph with existing setup, so 1000t at 75mph is not that far off with new traction motors.