Efficiency is a ratio of how much heat energy you put in to how much heat you get out the other end. The loss of efficiency occurs in the transfer. The question you want to ask in comparing ducted systems is how much heat will be lost from the square inches of surface of the duct vs the square inches of surface of the pipe.
A hot water pipe that is 1-inch in diameter has about 4 square inches of surface or about 1 square foot of surface per 36 running feet of pipe.
A duct to carry the same amount of heat in air handles 1400 cfm of air through a cross-section of abut 300 square inches; however, the same duct to carry the 5-ton air conditioning has to have a cross-section of 500 square inches to carry 2000 cfm. The square root of 500 is about 22 inches on a side or 4 times 22= 88 inches per linear inch of duct. Thirty-six running feet of that duct would have 36x12x88=38,000 square inches or / 144 = 264 square feet of surface.
There would be 264 times more surface of a duct than a pipe to carry the same heat. The emissive output of a square foot of surface at 120F (let us say that the medium is 120F) might be 100 btuh per square foot, then the pipe would 'lose' 100 btuh in 36 feet and the duct 26,400 btuh in 36 feet. This means the duct is 264 times more costly than the pipe for the same length. NOT using ducts as often as possible is a money-saver, thus the increase in number of ductless-split cooling units.
Warm air heat grew rapidly in the 1960's because people didn't know and didn't care about the cost of heat (being cheap gas and oil at the time) and very few people understand this efficiency loss from the surface of a duct. (If each joint of the duct is not masticked and taped to assure no air loss the actual efficiency is about 50%).
Whether air or radiators, as soon as the heat leaves, they are 100 percent efficient. However, air heat is less efficient AND less effective because convecting air tends to rise so you will need ceiling fans to move the heat downward as the warm air rises to the ceiling as it is blown into the room. Unless you put air registers below the windows the cold air will cross the room at the floor making a chill. To think about it, cooling partially involves creating a 'wind chill', so warm air heat continues that while warming. Heat pump owners are very familiar with the cold feeling while the heat is on.
Baseboard heat warms the walls and windows BEFORE they become cold. As the heat rises up the walls the heat is expended, some of the heat is sent through the air directly to the occupants as radiation (that is why they are called radiators. There are no warm air radiators.) That is why baseboard heated people in the northeast continent still have radiators after 100 years and baseboard after 60 years if they can afford it. They typically keep their thermostat at 68F, while warm air people put their thermostat at 74F, and heat pump people wear a sweater most of the winter.
As to two-stage or other burners, Weil McLain makes a modulating-input gas boiler called the Ultra that can be installed at 250,000 btuh input, but modulates down to about 60,000 btuh and between that for any demand. It runs at about 94% efficiency and can handle all of your house heat - and hot water needs through an indirect water heater tank. One long-lasting burner for all is a lot easier to service than a few short-lived heaters.
You can do a Google search for Freus prices and others. The best way to get a quote is through the estimators of the companies that will do the work. You might get some sharp installers by calling the companies whose equipment you might use. Some of the manufacturing majors will even lay out the installation for you so you have engineered plans for the installation to be done by tradesman subcontractors and there might be some possibility of 'marketing' opportunities for them in showcasing the installation.