Jojoe, I think you may be misunderstanding what’s going on. When you reduce the temperature on the boiler, it just shuts off the burner earlier to keep the water output at whatever temperature you set it. Nothing to do with the flow rate which is controlled by the pump setting. Lower temperature in the rads will give less heat to the room as you’ve found. As the weather gets colder, the water in the rads will need to be hotter. For now, I would knock the temp up to 60. If that doesn’t heat you room enough, increase it some more.
The effect on gas consumption by reducing boiler temperature isn’t really that much in practice but I do it and prefer rads not to scalding hot when they don’t need to be!