http://www.youtube.com/watch?v=XWpyNcoOyesReally love this matchup. Bromell has been a long time favorite, his form was something I thought was really intriguing a few years back. He had this perfectly upright, hips perfectly stable sort of form that no one else did.
It looks like recently he has taken a more rounded upper back to utilize the upper traps to help with the arm swing, which I'm not sure about. Intuitively I believe it could lengthen the arm swing at the start to better counterbalance the longer GCT's of the leg drive, but I could be wrong.
Lyles has a kind of elegance to his run, have some theories but not certain of any of them, so will not share. What I can say definitively though: compare their knee action and angles at the last 10m at the peak of their swing phases.
I think Lyles has a kind of looseness at that joint at that moment, and longer strides with possibly a slight APT related to that.
Bromell keeps the knee tight at peak swing phase, and that relates to shorter strides, higher stride frequency, and more PPT. I think there's something to both techniques. I do believe that Lyles technique is more energy efficient, which makes sense given his 200m prowess.