Rotorspeed - a. very definitely.
There seem to be a lot of people who want to only use a helicopter like an airliner and deny the true flexibility it gives us.
The fixation on the 50 kt Vmini (common to many helos), whilst a recognition of the inaccuracies of the pitot-static system, ignores the benefit a low velocity indicator (whether based on doppler, intertial nav or whatever) brings to the party.
A vertical IF takeoff is a straightforward and safe manoeuvre, but only when practised regularly. It certainly wouldn't have cost 4 lives if they had used that technique in Norfolk - regardless of the legalities.