Steven got his first powers from positive emotions, easy/safe stuff like a shield, a bubble, floating.
Steven's getting his new powers from negative emotions.
Pink-mode seems to be triggered by anger.
Super-speed seems to be triggered by.... impatience? Desperation?
Of course, these would be subjective, as more experience with the power allows it to be used sans emotion. After all, Steg used pink-mode during his power ballad.