Fully implemented limiter subroutine decreases internal accelerator position value, speed ↑ results in accelerator pos ↓, overriding driver demand.
This way there’s no precise vmax threshold, it rather depends on overall resistance, meaning higher vmax going downhill. Max limited vehicle speed seems to match manufacturer specified top speed, ~205 km/h for Impreza on flat road.
Of course, this limiter functionality allows for adjustments, by modifying the logic it can also be disabled entirely.
In all Euro4 ROMs seen so far, above limiter logic is preparatory and inactive.
We could insert necessary microcontroller instructions, making it work like Euro5 if someone really needs this.