3:50 That Hellbrute kill wasn't even close the fastest I have seen. If you have tactical with grenade launcher bolter-rifle and Heavy with the heavy plasma gun. It will die faster than you can manage to make heavy attack combo with your hammer.
using stim to heal the mortal wound like shown at 4:38 - is a noob way to do it :) pros keep stim to prevent loss of HP when there is no execution nor gunstrike for it.