David Orr made a YouTube video of his S&T variations and then asked me if I wanted to go to my 'The Golfing Machine" book and check out various sections and figure out what he's doing with his variations. Here's the video.
IMO, as the video progresses, it seems like he's going from a more straight line delivery path to some angled delivery path to a circular delivery path. I also believe he's going from more pitch elbow to punch elbow as the video moves along. I couldn't tell what exactly he was doing with his hips, but he noted that you can tell hip slide by axis tilt. Meaning more hip slide makes the spine tilt more (from the face on view).
I actually like his last swing the best, here's some frames of it.