There is no 'speed saturation' per se. One can design a locomotive either for heavy haul duties or high speed.
For a given power rating, a heavier loco will be able to heavy haul duties while a lighter loco will be better at high speed duties.
With both rated at almost 6000HP, the WAP7 and WAP5 are the best examples for this. The WAP7, heavier of the two at about tons, has a very good starting TE and can haul heavy rake but has poor acceleration beyond 50-60 kmph and practically no...
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hauling capacity beyond 140kmph. The WAP5, a very light loco at 78 tons, has relatively less starting TE and is not particularly great at low speeds, but beyond 60 kmph, starts to show much better performance than the WAP7.
The WAP7 can be made even faster, by reducing the loco's weight and playing with the gear ratio, but that will come at the cost of reduced hauling capacity.
There are many other parameters which make a WAP7 style design a poor choice for high speed operations.

There are no specs available for this loco right now, but based on some older documents from RDSO, we can speculate about the loco.
1) It is most likely a regular WAP5H with a power rating of 6125 HP.
2) The locos will be fixed to the rake, as in permanently attached at either end of the rake.
3) Since they are permanently attached...
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to the rake, there is no need of having a cab on one end of the loco. So, it will have a cab at one end and a vestibule at the other end.
4) The loco will be HOG enabled, but as it is supposed to be permanently coupled, only the vestibule end will have the HOG connectors. The cab end will not have the HOG IV connectors, but it will still have the UIC cable port available for those situations where the the train may have to be rescued by another loco.