also add following:
3)coupler strength limits maximum speeds
4)without Magnetic braking enabled not possible to reach speed of 250 safely
5)Higher weight makes them hauling with our conventional locos difficult as TE drops off rapidly at higher speed (thanks to field weakning in 3 phase locos) while the required TE rises rapidly owing to the parabolic relation between friction offered by winds and speed...
more... (or simply put, opposition by air friction is proportional to square of speed)