Would those numbers be typical?
Would Superior be using a "worst case scenario" "best case scenario" comparison when they compare a Fuel Oil furnace at 80% efficiency to a Propane burner at 95% efficiency?
80% for you existing boiler is certainly not worst case. If it was a low efficiency burner it'd be about 83% new so losing 3% is quite believable.
95% for new would be a top of the line model, the 90% I used for propane in my first post was for a non-condensing boiler. The price would obviously be higher for a condensing boiler at 95%.
80% oil would be costing you $39.30/MMBtu
95% propane would cost you $28.50/MMBtu
So switching would save you about 27.5% per year.