it all depends on a number of different considerations.
1.what kind of dancing and how experienced are the dancers.
here are some reasonably good dancing tempos metronome speeds for ceilidhs.
Irish Reels 200 to 212[easier to use 100 to 106].
irish/english jigs 108 to 120.
hornpipes for nottingham swing 143 to 150.
irish polkas 140to 143,Irish slides same,Marches 117 to 123.
solo step dancing Blackbird 140,or as stipulated by the dancer.
english polkas[with hop]jenny lind etc[108 to120]
fast irish hoppies [hornpipes or in england, scotland, keel row type]152 to160.
rapper jigs 135 to 140.
best thing is to watch the dancers.
all these speeds are not meant to be gospel,just an approximation.
old Swan Band were trying to make a point,because a lot of EFDSS dancers at that time were involved in bum scuffling[whisking through the dances too quickly to avoid stepping].
perhaps in hindsight they went to the other extreme,but the point had to be made.
some irish players play at a speed that is [imo]too fast,Iam not alone in thinking this Johnny oleary made the same point but he blamed the dancers.
I blame the dancers as well,however its not that simple,because many people who dont play for dancing also play at a sppeed that is too fast for dancing.