I'm probably wrong but I can't seem to find the thread that found this.
It's pinned above in the antonsirius thread, a few postings down, linked under dallter's tempo discussion (or something).
Anyways, some sad HD junkie ran the math for a whole world on tempo and it's affects. Produced many purty scatter-shot graphs that basically said there was no (or slight) tempo affects for everything BUT turnovers.
This was a ways back so maybe the sim engine has changed enough, or I'm hallucinating. I hate when that happens!