This may be slightly off topic, since i know nothing about MWSD, and i don't have exact tempo figures to share, but an observation - i've noticed recently that one of the moves in contra dance that is particularly sensitive to tempo issues is the hey, particularly when followed by a move like long waves balance & ROM. (You might notice this in dances such as "Rant & Roar" by Russell Owen and "Groovemongers Contra" by Don Flaherty). For ROM wave balances to work well, the tempo must be such that they can complete the hey and form waves ready to balance on the down beat of the next phrase. Conversely, particularly in a dance where a hey is followed by a balance & swing, when a tempo is too slow, dancers may finish a hey with a couple extra beats to spare before the balance. When there are live musicians involved, it strikes me that, whatever the starting tempo, musicians can respond to the dancers (and if they don't notice, callers can make sure they do) - particularly noting whether people are repeatedly late or early for the next move after a hey - or if dancers arrive early to a progression figure or appear to be rushing, all signs that the tempo needs adjustment.