Can you even heat (baseboard?) with such low water temps? Baseboard is designed for 600 BTU per foot at 180 degrees.

You can increase the differential 10-25 degrees if you want hotter water for longer runs, but most people keep it at 10 degrees. A setting of 10 means that your circulator will stop at 10 degrees below the low limit setting and restart at the low limit setting. A setting of 25 will restart the circ at 15 degrees above the low limit setting (for longer runs).

The differential setting is used to preserve hot water for the hot water coil.

Most boilers are set at 160/180 with a differential of 10 for baseboard and 15 for cast iron rads.

In the summer, you can turn the low limit down to 130-140 for domestic water use. Or turn it down all the way if you use a hot water heater.

Boilers are most efficient when they are in steady state operation. On the coldest day of the year, your boiler should run 24/7 and maintain the desired temps, if it is sized properly. Most are oversized. You can reduce the nozzle size for longer runs and more efficiency, but any changes have to be verified and tuned with a Bacarac kit.