I recently purchased a house so this is my first winter in it. The house was built in 1939 so most of the house is on a single heating zone using hot water radiated heat. The radiators are cast iron and recessed into the walls. However, there is an addition to the house circa early 2000's that uses baseboard hot water radiators. The addition also seems to be less heat efficient, probably because it has more windows, and has drywall instead of plaster. The addition is on a separate heat zone from the rest of the house. They are controlled by two different thermostats.
I'm trying to figure out how to set the thermostats to maximize heat efficiency. So far I've been assuming that the baseboards are less efficient than the cast iron radiators, and so I've been setting the thermostat for the addition far lower (about 5 degrees) less than the main thermostat. This basically means that the baseboards in the addition never switch on, and the addition remains cooler than the rest of the house (which is okay - it is a kitchen / dining room which we are okay with being cooler). The addition just gets heated via heat transfer from the other rooms.
Is this the best approach? Should I set the addition thermostat to the same temperature? What other considerations are there in order to balance my zones correctly to maximize energy efficiency?