Various cross-tunings were common, including ADAE, AEAE and AEAC#; these were of value to the dance fiddler, adding volume, harmony and ease of fingering. quote from above article
these are also used by American and Shetland fiddlers
A Sizeable proprtion of hornpipes in English and Irish REPERTOIRES were written by James Hill a scotsman who lived in England and wrote for competitions.
My experience has been that when playing in England and Scotland for dances like Belfast Duck and Nottingham Swing the tunes are swung quite heavily, more so than for hornpipes for irish sets, for irish sets i have found tunes like Keel row Some say the Devils dead, work better than say Plains of Boyle, then when it comes to playing for solo step dancing they are played swung.. somewhere between the two, and played very slowly to facilitate the intricate steps.
then there are different irish bowing styles, Donegal uses more bowing ornamentation and less left hand ornamention than Sliabh Luchra ,
in Sliabh Luchra, there is also octaving between two fiddles and for dancing more 2/4 polkas and slides , in Donegal there are Highlands which are an evolvement from Scottish Strathspeys
the 2/4 polkas are very differnt and have evolved from 4/4 polkas as are played for dance in England,
OF COURSE 4/4 POLKAS WERE ORIGINALLY MID EUROPEAN
all this shows that music has no boundaries and changes and evolves wherever it goes