I think a lot of Mercedes straight line speed come from it's trick rear suspension that, once above a critical speed, drops the rear ride height so much by going 'over-centre, it stalls the airflow over the rear diffuser reducing drag dramatically. Only really possible because of MB's low rake design.
Less drag is far more useful in gaining speed in the straights than increased bhp and it doesn't stress the power unit. Hopefully the MB engineers can tweak the transverse rear damper to match each of the remaining circuits.