In the long literature of criticism, we inherit the view that an essential attribute of all excellent conductors is their close attention to tempo, presumably in an attempt to recapture the composers' original conceptions of their music. I find in this study that it is not unusual for tempi in performances of an orchestral work to vary by as much as forty percent, even when composers provide tempo markings and in some cases with precise timing directions as well. Nevertheless, despite these large differences in total times spent on performances of a given work, and despite wide variety of styles and musical tastes, there often appears to be remarkable consensus on the temporal proportions of a work -- the fractions of time spent on its formal divisions. This is of course not surprising in music of constant metronomic tempo as, say, in a Beethoven scherzo. But the question becomes lively when we time performances of works that lend themselves to far greater temporal freedom -- the music of Mahler, Wagner, Debussy, Ives, Bartók, Schoenberg, and so on.
(Progress note: So far I have found no orchestral work that shows significant departure from this principle when performed by conductors whom we regard as differing widely in their approach to all other aspects of music. I'd appreciate comment from members with suggestions for pieces and conductors to test, and with reference to other work on this or related aspects of performance.)