(100/40) *100 = 250%, therefore the OL trains will be 250% the length of Canada line trains.
250% - 100% = 150%, in other words, the OL trains will be 150% longer, or 1.5* longer than the canada line trains
Everything you listed has barely anything or absolutely nothing to do with the mass of the vehicle, or actually improves with greater mass.
Tighter turning radii — Has to do with the length of the vehicle. Often this actually increases weight because you need more parts per car
Faster Acceleration/Deceleration — Has to do with tractive effort provided by the motors. Mass plays no role, power consumption does. In terms of getting up grades, it's the friction force, which increases linearly with mass.
Fewer Custom Parts — How does this have to do with mass? It's not like they're building the existing subway trains with special parts that are actually adding mass to the train. How is this magical new technology describe so much better than a subway train with 3rd rail collection? You cannot get more basic than that.