From what others have said, I may be getting exceptional performances out of my Heritage, but it's working well for me. It's not a great comparison, as I have 8' ceilings, but I heated my 2Ksf two-story house last year in Fairbanks, AK. From January on, not by choice, it was the sole heater, and I kept the place very comfortable most of the time--in fact, it did a better job than my oil-burning boiler had done.
Further pertinent details: our house is oriented towards the sun, with a lot of large windows on the south side, and not too many anywhere else. It's double-walled and well-insulated, earth-sheltered on the north side of the downstairs and part of the east and west walls as well.
Work/school days, I get a fire going in the morning, and come back to a house usually in the mid- to lower-60'sF, often with enough coals to get a fire going. I'll build up or restart a fire then, usually around six p.m., and do my run-up fire, and then let it back off a bit. At bedtime, I build a fire to burn overnight, and damp it down. If the dog insistts on going out in the night, I wander downstairs and enjoy the light show--at 3 a.m. the blue sheets of flam against the red coal of the wood is out of this world. By morning, I usually have coals to start up another fire; if not, I repeat until spring.
Longest useful-heat fire I got out of it was just under 12 hours, and it looked like it still intended to burn for awhile. It was -30F outside, and 65F inside. I posted about that, and someone else posted that I was, in fact, mistaken, that this didn't happen, so I'm guessing it doesn't happen all the time. As you get to know your stove, you learn how to coax a better performance out of it, how to lay a fire, what wood works best.
I did all this with some old piles of poplar left behind years before by the P.0., so it's not just in the wood.
I think a valid point of comparison is to find someone who's burning the stove you're thinking about, and compare their pre-wood-stove oil (or whatever you use) heating bill with yours. If you find a similar profile, that can help with decisions.
HTH, feel free to ask if I can be of assistance.