I think I finally found a good muscle rigging setup for Kish's shoulders. For this test, I rigged his right shoulder (camera left) and pectoral muscle with the muscle rig and left his other shoulder alone for comparison. I linked a camera to his body so that I could view the results throughout the entire sequence, and I think the muscle-rigged side is unquestionably better then the traditionally rigged side.
Of particular note is the sequence around frame 4350 where he has his arms up around his head. Before the muscle rig, there were issues with the shoulder twisting and shrinking in mass. The muscle rig fixed this. Also, around frame 7750 it is VERY apparent how much better the muscle rigged shoulder (Kish's right) is compared to the traditionally rigged shoulder (Kish's left).
Enjoy!