There is an awful lot of myth and rumour building up around these sets!
There is no need to isolate anything for 100mph running. Notch 5 is not being isolated. To do so would be rather daft: imagine the scenario of a failed power car - notch 5 isolated on the remaining good one would severely hamper performance and drivers are not permitted to poke around in the control cubicle reinstating notches.
In short, the only change to the power cars is to add the traction/brake interlock to prevent the set being moved with the sliding doors open. Everything else, such as motor gearing, control system, power rating etc etc is totally unchanged.