I got some tips and an edit for you.
When a hit doesn't dismember ( or doesn't dismember enough ) edit it(press "e" ). Sometimes an ankle or abs does the trick, or moving your shoulder. Experiment with things to build up momentum.
Be more relaxed. This is not a rule, but an advice. Don't relax all and move two joints, that'll make it look lazy, but try relaxing joints you don't need. Relaxed joints work like a whip, at first the go back, but then they swing forwards. This is good for your speed. In the edit below I relaxed the ankle ( and did loads of other things ) and got a nice crotchboom.
Your first hit was pretty potent if you'd edited it well. Example v v v