That said, though, that’s pretty much as emotional as he gets, and that’s sort of the power of scenes like this (pardon the Special Edition). You can just feel, from both David Prowse’s acting and the acting of all the Imperial Officers on the bridge with him, that he’s losing his mind with rage inside. His failure to take in Luke Skywalker has driven him past his breaking point.
On contrary, his clam and slow body motion, head gestures and walking pattern indicate the complete opposite. They indicate disappointment and inner conflict rather than rage or losing composure.
I agree that the scene indicates that he had a braking point, but definitely not a braking point in terms of rage or losing composure. The breaking point was that the encounter with Luke caused a conflict inside him that is then continued throughout the ROTJ. The ROTJ Vader (that some fans hate) actually started here in ESB.