From my limited experience, the number of participants and the number in each posse could be weighed to determine number of stages. For many, it's not the number of shots, but the amount of total time that matters. Fewer people - more stages. We could set up for six or seven and shoot fewer if a large number show. More set-up/take-down time, but the options are there when needed.
I hope the above makes sense.
Outlaw Sam Bass