I posted back in Oct with images showing the efficency of a hand fired stove when it is simmering along on a 40F day. You can see the hot air is much higher than the stack temps. Page up a few posts to see images.
Now, see below images on a cold day in the low 20's. These images from today. Last night I was pushing higher temps when ambient was in the teens. 300F hot air & 450F stack when outside temps were 17F. This hows how a hand fired stove will loose efficiency the harder it is pushed to create heat. My take on this trial, a hand fired stove is most efficient when burning at an easy simmer. Once you push the flames 6"+, heat will fly right up the stack, baro or no baro.
I've also performed tests with my baro set at .06w.c. thru .15"w.c. My conclusion is simple. The more the baro damper is open (.06), the less heat the stove will make. The more it is closed (.15), the more heat will be generated. Its all relative at a given outside temp & relative humidity. And as you create more heat, your firebox will empty sooner. Simple, right? I believe the baro damper will help for high winds & huge barometric changes to the atmosphere and or to make operation easier on an older maybe loose stove. This test was only performed using a Harman handfired, no stokers, no coal fired boilers.