There is fast rocksteady and slow rocksteady as well. Roland Alphonso discussed this and pointed out that there was fast ska and slow ska as well as fast & slow rocksteady. The framework or style the musicians were working with is what really changed. Kind of beside the point but interesting....Leonard Dillon commented that Train To Skaville was "part-way ska rock steady"/"Ska is not a matter of speed...it's a matter of arrangement"
DC
