Check out Winter's SC2 Low APM Challenge. He gets to the Masters league with all three races - using 100-120 APM in the diamond league, and way less in the lower leagues. He keeps emphasising how much of his "brain time" actually goes to decision making (he's also pretty good at explaining his thought process), and how much of the APM is actually just making units.

Most engagements are just: form a concave, pre-split/siege, cast a couple spells, a-move.