So! This might be a dumb question... But is there an actual performance benefit from using the "multMatrix" plus "decomposeMatrix" way of constraining things over using a normal Parent constraint?
I wanted to test this today as I need to rig a ton of nodes to my skeleton .. so I made a version using the matrix and the same setup with parent constraints. I then imported the file several times just so I had around 50 versions of the file in the scene.
I then select the skeleton hierarchy (for all instances) and rotate ALL joints.. Performance overall is the same it both versions, (with around 4 to 5 fps in viewport).
I realize this is by no means a thorough test .. but t still makes me wonder why the performance is roughly the same!