What about shots with no busy background? It is very difficult to tell the two apart. Compare this and the next image. The 85L is stopped down to f2.8 vs the STF @f2.8 (wide open, EXIF shows T4.5 as f4.5). Keep in mind this is not 100% done in lab testing standards. The STF being a longer lens should have shallower DOF, but the 85L is shot at a slightly closer distance.

Focus on the bokeh only!