I missed this post last Friday. I have the SF-250 too. But I reduce the firebox 50% this time of year. But typically I will open the damper anywhere between 1.5 turns thru 3 turns. Now, if it is warm and damp out, much more air will be required to maintain the fire.
Obviously you can build a really hot fire in this stove. But is is necessary? I allow my stove to simmer along therefore I have greatest efficiency. Right now, 50F ambient, 50% reducer installed, hot air out is 175F at the heat accumulator. Flue temp is 125F just below the baro which happens to be closed. 1.5 turns open on the damper.
If I want 300F hot air, I'll have to introduce much more air. But the flue temps will probably exceed the hot air. This takes me to the negative side of the efficiency chart, hot air vs. flue temp. Will be filling the box every 6 hrs too.